Columbia  ^uibersiitp 
in  tfje  Citp  of  i^eto  |9orfe 

^tljool  of  Bental  anb  #ral  burger? 


JSveferente  i^ibrarp 


PREFACE. 


In  deference  to  the  requests  of  many  of  his  students,  the 
author  pubhshes  this  work  in  the  form  of  lectures  as 
dehvered  by  him  at  the  New  York  Dental  School. 

It  is  in  no  way  intended  that  this  book  shall  take  the 
place  of  the  many  exhaustive  text  books  on  physiology, 
but  the  author  has  endeavored  to  present  to  the  dental 
and  medical  student  the  essentials  of  modern  physiology 
in  a  concise  form.  The  histology  and  anatomy  of  the 
viscera  are  only  considered  as  much  as  is  essential  for  the 
understanding  of  their  physiology. 

The  discussion  of  the  theories  regarding  certain  disputed 
questions  has  been  purposely  avoided,  and  only  the  gene- 
rally adopted  views  have  been  presented.  It  has  been 
thought  wise  to  omit,  as  far  as  possible,  the  description  of 
physiological  apparatus  and  experiments,  which  are  best 
understood  by  demonstration.  Drawings  have  also  been 
omitted  in  this  book,  as  the  lectures  throughout  the  course 
are  illustrated  by  drawings,  casts,  models,  lantern  projec- 
tions, and  experiments. 

This  book  is  also  intended  as  an  aid  in  the  preparation 
for  examination  by  dental-  and  medical-college  faculties 
and  State  examining  boards.  The  questions  and  exercises 
given  at  the  end  of  each  series  of  lectures  are  intended 


IV  PREFACE. 

to  familiarize  the  candidate  with  the  questions  asked  at 
the  faculty  and  State  Board  examinations. 

The  author  shall  ever  hold  in  grateful  regard  his  former 
teacher,  Prof.  Bernstein,  of  the  University  of  Halle,  under 
whose  guidance  his  studies  and  original  investigations 
were  made. 

In  the  preparation  of  these  lectures  the  following  authors 
were  freely  consulted  :  Gray,  Landois,  Du  Bois-Eaymond, 
Bernstein,  Foster,  Dalton,  Flint,  and  Kirk. 

A.  M. 

334  East  84th  street,  New  York  City, 
November,  1897. 


CONTEXTS  OF  LECTUEES. 


PAGES. 

Lecture  I., 1_6 

Introduction— Definitions  of  Terms — The  Cell  Theory 
— Protoplasm:  its  Composition,  Structure,  and  Prop- 
erties— The  Animal  Cell. 

Lecture  IL, 7_11 

Cell  G-eneration— Cell  Division — Karyokinesis— The 
Blastoderm — The  Blastodei^mic  !Membrane— The  Dif- 
ferentiation of  the  Cells. 

Lecture  III., 12-16 

The  Tissues:  Definition,  Classification— The  Epithe- 
lial Tissues:  their  Structure,  Varieties,  Distribution, 
and  Functions. 

Lecture  IV., 17-2S 

The  Connective  Tissues:  their  Classification  and 
General  Structure — White  Fibrous  Tissue :  its  Struc- 
ture, Distribution,  and  Uses — Yellow  Elastic  Tissue 
— Areolar  Tissue— Adipose  Tissue— Adenoid  Tissue — 
Cartilage,  Bone,  Dentin,  Enamel,  and  Cementum. 

Lecture  V., .'        .        .        .      24-29 

The  Muscular  Tissues:  Varieties  and  Structure — 
Nerve  Tissue. 

Appendix, 29-31 

Questions  and  Exercises  on  the  Cell,  the  Cell  Theory, 
and  the  Tissues. 

Lecture  VI., 32-40 

The  Physiology  of  the  Blood. 

Lecture  VII. , 41-49 

The  Physiology  of  the  Blood  (continued). 


vi  CONTENTS   OF   LECTURES. 

PAGES 

Lecture  VIIL, 50-55 

The  Physiology  of  the  Blood  (continued). 

Appendix, 55-59 

Questions  and  Exercises  on  the  Physiology  of  the 
Blood. 

Lecture  IX., 60-68 

The  Proximate  Principles. 

Lecture  X., 69-79 

The  Proximate  Principles  (continued). 

Appendix, 79-81 

Questions  and  Exercises  on  the  Proximate  Principles. 

Lecture  XI., 82-93 

Nutrition— Food— Composition  and  Nutritive  Value 
of  the  Various  Food  Materials. 

Appendix, 93-96 

Questions  and  Exercises  on  Food. 

Lecture  XII.,  97-106 

Digestion:  Definition  of,  Stages  of— The  Digestive 
Apparatus  —  Prehension  —  Mastication  —  The  Buccal 
Cavity— The  Teeth:  their  Structure  and  Develop- 
ment—The Muscles  of  Mastication— The  Nervous 
Mechanism  of  Mastication. 

Lecture  XIII., 107-115 

Insalivation— The  Salivary  Glands:  their  Structure, 
Nerve  and  Blood  Supply,  and  their  Secretion — The 
Saliva:  its  Composition  and  Uses;  the  Nervous 
Mechanism  of  its  Secretion. 

Lecture  XIV., 116-125 

Deglutition— The  Tongue,  Soft  Palate,  Pharynx,  and 
CEsophagus— The  Process  and  the  Stages  of  the  Act 
of  Deglutition— The  Nervous  Mechanism  of  the  Same 
— Stomach  Digestion— The  Stomach:  its  Structure, 
Nerve  and  Blood  Supply. 


CONTEXTS    OF   LECTURES.  Til 

PAGES. 

ILecture  XV 126-133 

Stomach  Digestion  (contirmed) — The  Gastric  Juice: 
its  Composition,  Physical  and  Chemical  Properties, 
and  Uses— Digestion  of  Various  Food  Articles  in  the 
Stomach — The  Nervous  Mechanism  of  the  Stomach — 
The  Act  of  Vomiting. 

lECTUEE  XVI., 131-142 

Intestinal  Dige.stion — The  Intestinal  Canal :  Its  Ana- 
tomy and  Structui'e — The  Succus  Entericus:  its 
Composition.  Chemical  and  Physical  Properties;  its 
Actions  and  Mode  of  Secretion — The  Pancreas:  its 
Structure — The  Pancreatic  Juice. 

Lecture  XVII  , 113-151 

Intestinal  Digestion  (continued) — The  Liver:  its 
Anatomy,  Structure,  and  Functions — The  Bile:  its 
Composition,  Physical  and  Chemical  Properties;  its 
Uses  and  Mode  of  Secretion. 

Lectur^^  XVIII 152-158 

Resume  of  the  Digestive  Processes  in  the  Intestinal 
Canal — Bacteria  in  the  Intestinal  Canal — The  Fa?ces: 
their  Formation  and  Quantity — ^^The  Act  of  Defa?cation. 

Appendix, 159-165 

Questions  and  Exercises  on  the  subject  of  Digestion. 

Lecture  XIX., 166-173 

The  Absorption— The  Channels  of  Absorption — The 
Villi:  their  Stri;cture  and  Function — The  Lymphatic 
System :  its  Distribution,  Structure,  and  Uses — The 
Lymph:  its  Origin  and  Composition — The  Chyle  and 
its  Composition — The  Factors  of  the  Lymph-circula- 
tion. 

Lecture  XX 173-179 

The  Absorption  (continued) — The  Factors  of  the  Ab- 
sorption —  Diffusion  —  Endosmosis  —  Filtration  —  The 
Materials  absorbed  by  the  Lymph-  and  Blood-vessels. 

Appendix, 179-182 

Questions  and  Exercises  on  Absorption. 


viii  CONTENTS   OF  LECTURES. 

PAGES. 

Lecture  XXI 183-193 

The  Circulation — The  Heart  and  its  Structure— The 
Arteries  and  their  Structure— The  Capillaries— The 
Veins. 

Lecture  XXII 194-206 

The  Action  of  the  Heart — The  Nervous  Mechanism  of 
the  Heart — The  Heart-sounds — the  Blood-pressure  — 
The  Factors  of  the  Circulation  of  the  Blood  through 
the  Heart,  the  Arteries,  Capillaries,  and  Veins— Nerv- 
ous Mechanism  of  the  Blood-vessels. 

Lecture  XXIII., 207-215 

Circulation  (continued)— The  Pulse — The  Sphygmo- 
graph — The  Sphygmogram — The  Foetal  Circulation 
and  the  Foetal  Circulatory  Apparatus. 

A}:)pendix, 216-218 

Questions  and  Exercises  on  the  Cii'culation. 

Lecture  XXIV., 219-227 

Respiration:  Definition — The  Respiratory  Apparatus: 
its  Anatomy  and  Structure— The  Mechanism  of  Res- 
piration—Muscles of  Respiration — Types  of  Respira- 
tion— Chest-capacity  —  Breathing-capacity—  Quantity 
of  Air  in-  and  exlialed  by  Simple  and  Forced  Respi- 
ratory Movements— Number  of  Respirations — Quan- 
tity of  Air  required  in  Twenty-four  Hours — Quantity 
of  Oxygen  required — Quantity  of  COa  exlialed  in 
Twenty-four  Hours — Quantity  of  Watery  Vapor  ex- 
haled. 

Lecture  XXV., 228-233 

Composition  of  Atmospheric  Air  —  Respiratory 
Changes  of  the  Air— Law  of  the  Diffusion  and  Disso- 
ciation of  Gases— The  Gases  of  the  Blood — Tiie  Ten- 
sion of  the  Gases. 

Lecture  XXVI. , 234-241 

Nervous  Mechanism  of  the  Act  of  Respiration— At- 
mospheric Pressure. 

Appendix, 241-244 

Q  leslions  and  Exercises  on  Respiration. 


CONTENTS   OF   LECTL'RES.  IX 

PAGES. 

Lecture  XXVII., .  245-253 

Assimilation  and  Dissimilation — Origin  of  the  Blood 
and  Lympli-ingredients— The  Spleen:  its  Structure 
and  Functions — The  Glj^cogenetic  Function  of  the 
Liver — The  Structure  and  Functions  of  the  Thyroid 
and  Thymus  Glands,  and  of  the  Suprarenal  Capsules. 

Appendix, 253-254 

Questions  and  Exercises  on  the  Assimilation  and  Dis- 
similation. 

Lecture  XXYIII., 255-266 

The  Excretions — The  Kidneys:  their  Anatomy  and 
Structure — The  Eenal  Circulation — The  Urine:  its 
Composition.  Chemical  and  Physical  Properties — The 
Ingredients  of  the  Urine:  their  Character  and  Oi'igin. 

Lecture  XXIX., 267-278 

Mode  of  Excretion  of  the  Urine— Conditions  Influenc- 
ing it— The  Anatomy  and  Structure  of  the  Ureters, 
Bladder,  and  Urethra — The  Act  of  Micturition— Sweat- 
glands:  their  Structure  and  Functions — Sweat:  its 
Chemical  and  Physical  Properties,  Composition, 
Mode  of  Secretion— Conditions  Influencing  it. 

Appendix, 278-280 

Questions  and  Exercises  on  the  Excretions. 

Lecture  XXX., 281-290 

The  Secretions— Human  Milk — The  Mammary  Glands : 
their  Structure  and  Functions— The  Tears —The  Lach- 
rymal Apparatus — The  Secretions  of  the  Membranes 
— The  Structure  and  Functions  of  the  Membranes — 
Genei-al  Structure  of  the  Secretory  Glands— The  Skin 
and  its  Functions- The  Hairs  and  Nails. 

Appendix, 290-291 

Questions  and  Exercises  on  the  Secretions  and  the 
Skin'and  its  Functions. 

Lecture  XXXL, 292-300 

Animal  Heat. 

Lecture  XXXII. , 301-307 

Animal  Motion— The  Physiology  of  Muscle. 


X  CONTENTS   OF   LECTURES. 

PAGES. 

Lecture  XXXIII., .  308-315 

Ciliary  Motion— Protoplasmic  Motion. 

Appendix, 315-317 

Questions  and  Exercises  on  Animal  Heat  and  Animal 
Motion. 

Lecture  XXXIV., 318-324 

The  Physiology  of  the  Nervous  System — The  Nerve 
Centres :  their  Structure  and  Functions. 

Lecture  XXXV., 325-33a 

The  Structure,  Classification,  Properties,  and  Func- 
tions of  Nerve-fibres. 

Lecture  XXXVI. , 334-346 

The  Brain— The  Cerebrum:  its  Anatomy. 

Lecture  XXXVII. , 347-35& 

The  Cerebrum:  its  Anatomy  (continued). 

Lecture  XXXVIII. , 359-366 

The  Structure  of  the  Cerebrum. 

Lecture  XXXIX., 367-377 

The  Functions  of  the  Cerebrum. 

Lecture  XL., 378-385 

The  Cerebellum:  its  Anatomy,  Structure,  and  Func- 
tions— The  Pons  Varolii:  its  Anatomy,  Structure, 
and  Functions, 

Lecture  XLL, 386-400 

The  Medulla  Oblongata:  its  Anatomy,  Sti-ucture, 
and  Functions — The  Fourth  Ventricle  of  the  Brain. 

Lecture  XLIL, 401-410 

The  Cranial  Nerves  (First  to  Fifth  Pair,  inclusive). 

Lecture  XLIII., 411-417 

Tlie  Cranial  Nerves  (Sixth  to  Twelfth,  inclusive). 

Lecture  XLIV., 418-42a 

The  Spinal  Cord:  its  Anatomy,  Structure,  and 
Functions. 


CONTENTS   OP   LECTURES.  XI 

PAGES. 

Lecture  XLV., 429-434 

The  SpinaljNerves— Sympathetic  Nervous  System. 

Appendix, 434-436 

Questions  and  Exercises  on  the  Anatomy,  Structure, 
and  Physiology  of  the  Nervous  System. 

Lecture  XL VI., 437-443 

The  Senses  and  the  Sensory  Organs. 

Lecture  XLVIL, 444-450 

The  Senses  and  the  Sensory  Organs  (continued). 

Lecture  XLYIIL, 451-462 

The  Senses  and  the  Sensory  Organs  (continued). 

Appendix, 

Questions  and  Exercises  on  the  Senses  and  Sensory  463 
Organs, 

Lecture  XLIX., 464-471 

The   Generative  Organs  and  the  Sexual  Products  of 
the  Male  and  Female. 

Lecture  L., 472-480 

Fecundation  of    the    Ovum — Development    of    the 
Fecundated  Ovum. 

Lecture  LL, 481-490 

The  Development  of  the  Foetus. 

Appendix, 491 

Questions  and  Exercises  on  Generation  and  Develop- 
ment. 


LECTTJEE  I. 


INTRODUCTION. 


Ladies  and  Gentlemen: 

Physiology  is  the  scieDce  which  treats  of  the  normal 
functions  of  hving  organisms. 

The  human  hocly  is  a  complex  structure  of  organs,  each 
possessing  different  functions,  whose  combined  activity 
constitutes  life.  The  study  of  life,  called  biology,  com- 
prises three  subjects. 

1.  Morphology,  which  is  the  study  of  the  structure  of 
the  organs,  may  be  either  macroscopical — by  means  of  the 
unaided  eye — or  microscopical.  The  former  is  termed  vis- 
ceral anatomy,  and  the  latter  histology.  2.  Physiology, 
which  treats  of  the  functions  of  the  organs.  3.  The  study 
of  the  growth  and  development  of  the  organism,  termed 
embryology . 

Physiology  is  studied  by  experiment  and  by  observation , 
It  is  essential  to  comprehend  thoroughly  the  fundamental 
chemical  and  physical  laws  and  the  anatomy  and  histology 
of  the  organism. 

Up  to  a  century  ago  comparatively  little  was  known  of 
histology,  but  since  then  scientists  have  been  able,  due  to 
the  constant  improvement  in  mechanical,  electrical,  and 
optical  appliances,  to  study  the  subject  with  better  and 
more  definite  results. 

The  first  description  of  the  structure  of  tissues  was  that 
of  Holland,  who  stated  that  they  were  composed  of  fibres. 
Soon  after  that   Ediuards  advanced  his  globular  theory^ 
1 


■2        LECTURES   ON   HUMAN    PHYSIOLOGY   AND   HISTOLOGY. 

At  the  beginning  of  this  century  the  botanist  Schleiden 
detected  that  the  tissues  of  plants  were  composed  of  ele- 
ments which  he  called  cells,  and  which  he  described  as 
microscopical  bodies  consisting  of  a  limiting  membrane, 
within  this  a  homogeneous  substance,  and  in  the  middle 
of  this  a  more  solid  body,  the  nucleus. 

In  1837  Theodore  Schivann  found  in  animal  tissues  ele- 
ments similar  in  structure  to  the  cells  of  plants.  Further 
investigations  showed  that  all  animal  tissues  are  composed 
of  elements  which  are  called  cells,  and  that  to  these  the 
vital  functions  of  the  tissues  must  be  attributed. 

THE   CELL. 

The  animal  cell,  as  Schwann  described  it  first,  is  a  micro- 
scopical body  which  manifests  vital  properties,  and  which 
consists  of  a  cell-wall  or  limiting  membrane  enclosing  a 
homogeneous  mass,  the  cell-contents  or  cell-body,  in  the 
centre  of  which  is  a  small  body,  the  cell-nucleus. 

With  the  aid  of  better  instruments  it  was  observed  that 
not  all  cells  have  a  cell- wall.  Max  Schultze  believed  this 
to  be  merely  the  product  of  retrogressive  changes  in  the 
■cell-contents,  and  that  the  only  essential  constituents  of 
a  cell  are  the  cell-contents,  or  cell-body,  and  the  nucleus; 
further  observations  revealed  the  fact  that  some  of  the 
lower  forms  of  animal  and  plant  life  are  composed  only 
of  a  homogeneous  mass  having  no  cell-wall  and  no  cell- 
nucleus,  and  still  exhibiting  vital  functions. 

This  demonstrates  what  is  now  almost  universally  be- 
lieved, that  the  substance  composing  the  cell-body  is  the 
•only  essential  constituent  of  the  cell,  and  that  to  it  alone 
the  vital  properties  of  the  cell  must  be  attributed.  This 
substance  has  received  various  names,  as  blastema,  sarcode, 
germinal  matter,  bioplasm — as  it  was  called  by  Beale,  of 
this  country— protoplasm,  or  first  formed  matter,  as  it  was 
called  by  Schultze.  All  these  designate  the  same  thing — 
namely,  the  living  matter  of  a  cell. 


INTRODUCTION.  6 

THE  PROPERTIES  OF  PROTOPLASM. 

The  protoplasm,  which,  as  has  been  stated  before,  is  the 
living  matter  of  a  cell,  possesses  certain  vital  pi:operties 
which  are  common  to  protoplasm  wherever  it  is  found. 
These  general  properties  are  motion,  sensation,  nutrition, 
and  reproduction. 

The  amceba,  a  microscopical  unicellular  animal  organism 
living  in  the  sea  water,  may  be  well  used  to  demonstrate 
the  vital  properties  of  protoplasm.  The  amoeba  represents 
the  lowest  form  of  animal  life ;  it  consists  merely  of  a  mass 
of  protoplasm,  and  has  neither  limiting  membrane  nor 
nucleus.  If  the  amoeba  is  examined  under  the  microscope, 
it  will  be  seen  to  possess  the  power  to  thrust  outward  from 
its  main  mass  processes  either  lobular  or  pointed  and 
eloDgated  in  form.  These  processes  are  termed  pseudo- 
podia;  they  adhere  to  other  bodies  and  places  toward 
which  they  are  projected,  and  then  draw  the  main  portion 
forward,  thus  changing  the  position  of  the  whole  mass. 

A  similar  form  of  locomotion  is  observed  in  cells  in  the 
human  body  ;  it  is  termed  amoeboid  motion. 

Other  forms  of  motion  observed  in  animal  cells  are  the 
* '  Brownian  "  and  the  ciliary  motions.  It  has  been  observed 
that  the  particles  of  a  cell  are  in  constant  molecular  mo- 
tion ;  this  was  first  described  by  Brown,  hence  the  name 
"  Brownian  motion."  In  many  parts  of  the  body  minute 
hair-like,  protoplasmic  processes  are  projected  from  the 
free  surfaces  of  the  cells  ;  these  processes  have  a  rapid 
vibratory  motion  and  are  called  cilia,  hence  the  name 
"  ciliary  motion."  That  protoplasm  possesses  the  property 
of  sensation  is  shown  by  experiments.  External  conditions, 
such  as  change  of  temperature,  the  application  of  certain 
chemicals,  electricity,  the  alternation  of  darkness  and 
light,  mechanical  irritation,  etc.,  wiU  influence  the  activity 
of  the  protoplasm.  It  has  been  observed  that  increase 
of  temperature  increases,  and  decrease  of  temperature  de- 
creases, the  mobility  of  the  amoeba,  and  that  the  application 


4        LECTURES    ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

of  certain  chemicals  produces  contraction.  All  this  tends 
to  sho^v  that  it  possesses  the  property  of  sensation. 

The  amoeba  obtains  its  materials  for  nutrition  by  thrust- 
ing out  from  its  body  processes  which  grasp  and  envelop 
the  substances  the  animal  has  selected  for  its  food,  and 
thus  takes  them  up  into  its  body,  where  they  undergo  a 
process  of  assimilation  and  serve  purposes  of  nutrition,  as 
is  shown  by  the  growth  of  the  amoeba. 

The  cells  of  the  animal  body  take  their  materials  for 
nutrition  from  the  exudation  of  blood  constituents  into  the 
interstices  of  the  tissues.  Protoplasm  possesses  the  prop- 
erty of  reproducing  its  own  kind. 

When  an  amoeba  has  attained  a  certain  size  it  shows  a 
tendency  to  divide.  The  process  begins  by  a  constriction 
at  the  centre  ;  this  continues  until  the  amoeba  assumes  an 
hour-glass  shape,  and  finally  separates  into  two  distinct 
amoebae,  each  possessing  the  same  vital  properties  as  the 
parental  body. 

THE  STRUCTURE  OF  THE  ANIMAL  CELL. 

In  the  higher  animal  organism  the  cells  are  mostly  found 
to  consist  of  a  cell-body  and  a  cell-nucleus, 

THE    CELL-BODY. 

The  cell-body  or  cell-contents  is  composed  principally 
of  proteid  substances,  the  exact  nature  and  molecular 
structure  of  which  are  not  exactly  known ;  these,  together 
with  water,  inorganic  salts,  and  occasionally  some  fatty 
matter  and  carbohydrate  material,  form  a  generally  color- 
less, transparent,  semi-solid  substance  which  possesses  the 
vital  properties  described  above.  The  cell-body  shows 
generally  a  distinct  structure  consisting  of  a  delicate  fibril- 
lar reticulum  holding  in  its  meshes  a  more  liquid  sub- 
stance. Examined  with  a  high  power  it  will  be  seen  that 
the  delicate  fibrillge  forming  the  intracellular  reticulum 
are  composed  of  minute  granular  bodies  called  microsoms ; 


INTRODUCTION.  5 

and  it  is  believed  that  to  them  the  more  important  vital 
processes  of  the  cell  must  be  attributed.  These  microsoms 
constitute  particularly  the  substance  of  the  cell-body,  called 
protoplasm,  while  the  substance  contained  in  the  meshes 
of  the  fibrillar  reticulum  is  called  paraplasm,  to  which 
more  inferior  physiological  properties  are  attributed.  In 
the  cell-body  there  are  sometimes  found  small  cavities 
called  vacuoles ;  they  are  mostly  seen  in  the  secreting  cells 
and  generally  contain  fluid.  In  other  cells  such  substances 
as  pigment,  fat,  glycogen,  and  crystals  are  seen  in  the  cell- 
body. 

THE   CELL-NUCLEUS. 

The  animal  cell  has,  with  few  exceptions,  a  nucleus. 
This  is  a  minute  body  situated  within  the  cell-body  and 
generally  shaped  like  the  cell  itself. 

The  nucleus  has  a  complex  structure  similar  to  that  of 
the  cell-body  ;  it  consists  of  a  limiting  membrane  enclosing 
a  reticulum  composed  of  delicate  fibrillce,  in  the  meshes 
•of  which  is  found  a  liquid  substance.  The  fibrilla?  are 
composed  of  minute  granular  bodies  called  microsoms, 
which  are  embedded  in  a  substance  caUed  linin.  The 
limiting  membrane  and  the  microsoms  are  composed  of  an 
albuminoid  substance  belonging  to  the  class  of  nucleins. 
This  substance  has  a  great  affinity  for  coloring  agents, 
such  as  methyl  blue,  Vesuvian  brown,  etc.,  and  it  is  for 
this  reason  also  called  chromatin.  The  linin  in  which 
the  microsoms  are  embedded,  and  the  liquid  substance 
•contained  in  the  meshes  of  the  fibrillar  network,  possess 
no  affinity  for  coloring  agents  and  are  therefore  called 
acliromatin.  The  liquid  substance  in  the  meshes  of  the 
intranuclear  network  is  also  called  paralinin  or  nucleo- 
plasm. 

In  the  cell-nucleus  there  are  sometimes  seen  minute 
bodies  which  also  possess  an  affinity  for  coloring  agents  ; 
i3ome  of  these  are  destroyed  by  such  agents  as  will  destroy 


6         LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

chromatin  substance.  They  are  consequently  only  small 
collections  of  this  material,  and  are  called  false  nucleoli. 
Again,  some  of  these  minute  bodies  are  not  destroyed  by 
agents  which  destroy  chromatin  matter ;  these  are  called 
true  nucleoli;  they  are  composed  of  an  albuminoid  sub- 
stance cdll^di  par  anuclein. 


LECTrRE   II. 

In  my  last  lecture  I  described  the  structure  and  the 
general  physiological  properties  of  cells,  and  the  next  ques- 
tion which  arises  is — How  do  the  cells  originate  i 

Up  to  nearly  forty  years  ago  the  theory  of  a  spontaneous 
cell-generafion  was  held:  it  was  supposed  that  particles  of 
matter  collected  and  spontaneously  developed  into  a  cell. 
It  was  in  1S5S  that  RudoJjjh  VircTiov:.  Professor  of  Surgical 
Pathology  at  the  University  of  Berlin,  advanced  his  state- 
ment that  all  cells  arise  from  a  pre-existing  cell;  this  state- 
ment is  precisely  defined  by  his  well-known  dictum.  •"'  Om- 
nis  cellula  e  cellula,''  which  means  "  All  cells  from  a  cell.'^ 
It  is  this  theory  which  is  now  almost  universally  acknow- 
ledged. 

CELL-DIVISION. 

The  cells  of  the  tissues  of  vertebrates,  including  man. 
arise  by  the  conjugation  of  the  female  ovum  with  the  male 
cell,  called  the  spermatozoon.  The  cells  of  the  higher  ani- 
mal organisms  multiply  by  indirect  division — a  process 
which  begins  with  a  series  of  changes  in  the  cell-nucleus- 
and  is  called  mitosis  or  karyoldnesis.  The  process  may  be 
divided  into  distinct  phases,  which  are  termed  the  p7'0- 
phases,  metaphases,  and  anajyhases. 

In  describing  the  process  it  is  necessary  to  describe  the 
changes  which  take  place  in  the  chromatic  substance  of 
the  nucleus,  those  which  take  place  in  the  achromatic 
substance  of  the  same,  and  those  which  take  place  in  the 
cell-body.  These  changes  do  not  take  place  in  the  order 
stated  here,  but  occur  simultaneously  in  the  various  parts 
of  the  cell. 


8         LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

A.  Changes  taking  place  in  the  chromatic  substance  of 
the  nucleus. — The  first  noticeable  change  in  this  part  of  the 
nucleus  is  a  swelling  of  the  fibrillar  network  and  of  the 
limiting  membrane ;  then  the  latter  disappears  and  the 
fibrillar  of  the  reticulum  collect  into  a  coil,  called  spirem ; 
this  coil  is  composed  of  V-shaped  loops,  called  chromosoms 
or  chromatin  loops.  The  changes  thus  described  complete 
the  stage  of  involution. 

The  second  stage  consists  in  the  arranging  of  the  chroma- 
tin loops  in  the  form  of  a  rosette.  Then  the  chromatin 
loops  begin  to  separate  at  their  peripheral  portion  and  be- 
come more  angular  toward  the  centre.  This  results  in  the 
formation  of  a  number  of  V-shaped  chromatin  masses, 
which,  with  their  pointed  portions,  are  directed  toward  the 
centre,  and  by  this  arrangement  form  the  figure  of  a  star 
or  of  an  aster. 

This  third  change  in  the  chromatin  portion  of  the  nucleus 
is  termed  the  monaster  formation. 

The  fourth  stage  consists  in  the  longitudinal  division  of 
the  chromatin  portions  forming  the  monaster,  which  re- 
sults in  the  formation  of  two  sets  of  V-shaped  chromatin 
portions;  these  generally  separate  until  finally  two  stars  or 
asters  have  formed  in  the  cell-body.  This  process  is  known 
as  the  diaster  formation. 

Now  the  V-shaped  branches  of  the  two  stars  again  unite 
at  their  peripheral  ends  and  become  more  rounded  at  their 
angular  portion,  resulting  in  the  formation  of  two  rosettes. 
This  comprises  the  fifth  stage. 

The  next  change  consists  in  the  formation  of  two  con  vo- 
lutes from  the  chromatin  loops  of  the  two  rosettes.  Then 
appears  the  intranuclear  network,  and  finally  a  limiting- 
membrane  forms  around  each  of  the  two  nuclei  which 
have  developed  from  the  original  cell-nucleus.  This  re- 
sults from  the  series  of  changes  already  described,  which, 
for  a  clearer  understanding,  may  be  said  to  consist  of  seven 
stages,  as  follows: 


THE   ANIMAL  CELL.  9 

1.  Involution  or  spirem  formation. 

2.  Rosette  formation. 

3.  Monaster  formation. 

4.  Diaster  formation. 

5.  Double-rosette  formation. 

6.  Double-convolute  formation,  or  dispirem. 

7.  Formation  of  the  intranuclear  reticula  and  of  limiting 
membranes. 

B.  Changes  taking  place  in  the  achromatic  substance. — 
In  the  cell-body  there  are  seen,  prior  to  any  noticeable 
-changes  in  the  nucleus,  one  or  more  highly  refractive 
bodies,  called  centrosoms,  which,  according  to  some  au- 
thors, arise  from  the  protoplasm,  and  according  to  others 
from  the  achromatic  substance  of  the  nucleus.  The  cen- 
trosoms  are  surrounded  by  a  light  zone  consisting  of  rays 
which  radiate  toward  the  centrosoms.  This  is  known  as 
the  archiplasm  zone.  When  the  changes  in  the  chromatic 
substance  of  the  nucleus  are  noticeable,  it  will  be  seen  that 
the  centrosoms,  with  the  archiplasm  zones  surrounding 
them,  assume  a  position  on  either  side  of  the  nucleus. 
The  achromatic  substance  in  the  nucleus  now  arranges 
itself  into  transverse  rays,  which  become  continuous  with 
the  rays  of  the  archiplasm  zone.  As  the  chromatic  por- 
tion of  the  nucleus  begins  to  separate,  these  rays  also  pass 
transversely  between  the  two,  forming  nuclei;  and  as  the 
formation  of  these  completes,  the  rays  retreat  into  them 
and  form  their  achromatic  portion. 

C.  Changes  in  the  cell-body.  —While  the  changes  in  the 
€ell  progress,  as  described  above,  the  cell-body  becomes 
constricted  near  its  centre,  and  this  constriction  continues 
until  the  cell  separates  into  two  portions,  each  containing 
a  cell-nucleus.  The  centrosoms  are  visible  until,  and  even 
after,  the  completion  of  the  process  described. 

The  prophases  comprise  the  changes  which  take  place 
up  to  the  formation  of  the  monaster;  the  metaphases,  the 
•changes  which  take  place  up  to  the  formation  of  the  nuclei; 


10       LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

and  the  anaphases,  those  changes  which  take  place  up  to 
the  time  that  the  separation  of  the  cell  is  completed. 

Other  forms  of  cell-multiplication  which  are  observed  in 
the  animal  cell  are  the  direct  or  amitotic  and  the  hetero- 
typic.    They  are  seldom  observed  under  normal  conditions. 

We  have  already  described  the  structure  and  general 
functions  of  the  animal  cell,  and  the  process  of  the  multi- 
plication of  the  cells  as  it  is  observed  in  the  tissues  of  the 
higher  animal  organism.  The  cell,  after  it  has  formed, 
develops,  grows,  performs  its  functions,  and  finally  dies. 
The  latter  process  also  begins  with  certain  changes  in  thfr 
cell-nucleus,  and  is  called  karyolisis  or  chromatolisis. 

The  cell  from  which  the  cells  of  the  animal  body  arise  is 
the  ovum  of  the  female,  which,  after  its  conjugation  with 
the  male  cell,  segmentates.  The  cell  divides  and  subdi- 
vides by  the  process  described  above;  the  segmentation 
continues  until  a  mulberry- shaped  body,  called  the  hlasto- 
derm,  is  formed.  It  is  composed  of  a  collection  of  simple, 
round,  nucleated  cells,  called  emhryonic  cells.  The  cells  of 
the  blastoderm  now  arrange  themselves,  by  a  series  of 
changes  known  as  gastrulation,  into  layers  forming  a 
body  or  mass  called  the  blastodermic  membrane.  At  first 
two  layers  are  formed,  called  the  inner  and  outer  layers, 
and  later  on  a  third  or  middle  layer  appears.  The  outer 
layer  is  called  the  epiblast  or  ectoderm,  the  inner  layer  the 
hypoblast  or  endoderm,  and  the  middle  layer  the  mesoblast 
or  mesoderm.  Up  to  the  time  of  the  formation  of  the  blas- 
todermic membrane  the  cells  have  a  uniform  shape  and  no 
special  characteristic  properties.  At  the  period  when  the 
inner  and  outer  layers  of  the  blastodermic  membrane  are 
formed  its  cells  begin  to  differentiate.  They  now  assume 
the  various  characteristic  forms  which  we  find  in  the  cells 
of  the  various  tissues.  The  cells  may  be  classified,  accord- 
ing to  their  shape,  into  spherical,  2^olyhedral,  squamous, 
columnar,  ciliated,  branching,  and  spindle-shaped.  At  the 
same  period  when  these  cells  assume  characteristic  form& 


THE   ANIMAL   CELL.  11 

they  also  develop  special  functions  and  properties,  and, 
according  to  these,  the  cells  of  the  tissues  can  be  classified 
into  protecting,  secreting,  contractile,  sensitive,  and  motile. 

I  will  give  a  more  detailed  account  of  the  changes  which 
take  place  in  the  ovum  after  its  fecundation,  and  in  the 
development  of  the  structures  of  the  animal  body,  when  in 
the  course  of  my  lectures  I  reach  the  subject  of  embry- 
ology. 

In  my  next  lecture  I  shall  give  a  description  of  the 
elementary  tissues  together  with  their  physiological  pro- 
perties. This  is  essential,  as  these  tissues  enter  into  the 
construction  of  the  numerous  organs  of  the  animal  body. 
In  order  to  study  and  understand  their  physiology  a  thor- 
ough comprehension  of  their  histology  is  essential,  and  it 
is  for  this  reason  that  you  are  required  to  attend  a  course 
in  practical  histology. 


LECTURE  III. 

Before  beginning  a  description  of  the  tissues  I  will  state 
that  by  the  word  tissue  we  understand  a  collection  of 
cells  separated  hy  an  intermediate  substance. 

The  tissues  differ,  not  only  in  the  form  and  physiological 
characters  of  their  cells,  but  also  in  the  consistence  of  the 
intercellular  or  intermediate  substance,  which  may  be 
liquid,  semi-solid,  or  solid.  The  tissues  all  arise  from  the 
layers  of  the  blastodermic  membrane.  In  the  classification 
of  the  tissues  it  is  hardly  possible  to  consider  them  in  the 
order  of  their  genesis  from  the  various  layers  of  the  blasto- 
dermic membrane,  since  many  arise  at  different  times,  and 
not  always  from  one  layer,  but  from  the  different  layers 
of  the  blastodermic  membrane. 

In  my  description  I  shall  follow  the  following  classifica- 
tion : 

1.  Epithelial  tissues. 

2.  Connective  tissues. 

3.  Muscular  tissues. 
■1.  Xerve  tissue. 

.5.  Fluid  tissues,  viz.,  blood,  lymph,  chyle. 

I.    THE   EPITHELIAL   TISSUES. 

Epithelium  is  the  first  tissue  developed  from  the  layers 
of  the  blastodermic  membrane.  This  tissue  is  composed  of 
cells  of  various  forms,  which  are  superimposed  in  one  or 
more  layers  upon  a  basement  membrane,  called  the  mem- 
hrana  propria.  The  cells  are  connected  at  their  margins 
by  an  albuminous  intercellular  cementing  substance,  or  by 
processes  w^hich  form  the  so-called  intercellular  bridges  ; 


THE    EPITHELIAL    TISSUES.  13 

these  leave  open  spaces  between  the  cells,  filled  with  the 
fluid  from  which  the  cells  derive  their  nourishment. 

Epithelium  is  found  covering  all  free  surfaces  of  the 
body.  These  are.  the  membranes,  viz..  the  skin,  the  serous, 
synovial,  and  mucous  membranes:  thehniugsof  the  heart, 
blood  vessels,  lymphatics  and  all  glands,  the  hning  of  the 
ventricles  of  the  brain  and  of  the  central  canal  of  the  spinal 

cord. 

Tlie  Functions  of  the  Epithelial  Tissues. 

Epithelium  has  various  functions,  and  may  accordingly 
be  classified  as: 

A.  Protecting  epithelium — that     covering    the    mem- 
branes and  the  lining  of  the  closed  cavities. 

B.  Secreting  epithelium — that  covering  the  lining  of 
the  glands. 

C.  Protecting,    secreting,   and  absorbing  epitheliiun — 
that  covering  the  lining  of  the  alimentary  canal. 

D.  Sensory  epithelium — that   covering   the   Schneide- 
rian  membrane. 

E.  Motile  epithelium — the  cihated  epithehum. 

The  epithehal  tissues  are  found  to  differ  in  structure  in 
the  various  locations  in  the  body,  and  are  divided  into  four 
groups — namely : 

(a)  Simple  epithelium. 

(6)  Stratified  epithehum. 

(c)  Transitional  epithelium. 

(cT)  Glandular  epithelium. 
The  epithelium  covering  the  hning  of  the  closed  cavities 
— viz.,  the  heart,  blood-vessels,  the  ventricles  of  the  brain, 
the  spinal  canal,    etc.— is    called    the  endothelium;    this 
belongs  to  the  variety  of  simple  epithelium. 

(a)  Simple  Epithelium. 

This  variety  is  made  up  of  a  single  layer  of  epithelial 
cells  supported  by  a  basement  membrane.  This  is  found 
covering  the  synovial  and  serous  membranes,  the  mucous 


14       LECTURES  ON   HtJMAN   PHYSIOLOGY   AND    HISTOLOGY. 

membrane  lining  the  greater  part  of  the  intestines  and 
the  air-passages,  and  the  endothehal  Hning  of  the  closed 
cavities.  The  cells  of  the  simple  epithelium  are  either  flat, 
columnar,  or  cubical  in  shape,  and  are  ciliated  in  certain 
parts  of  the  body. 

Flat,  pavement,  or  tessellated  simple  epithelium  is  found 
covering  the  serous  and  synovial  surfaces.  The  endothe- 
lial lining  of  the  heart,  blood-vessels,  lymphatics,  etc.,  also 
consists  of  a  single  layer  of  flat  cells.  The  cells  are  gene- 
rally many-sided  and  present  a  tiled  appearance.  Their 
sides  are  cemented,  and  each  cell  has  generally  a  distinct 
nucleus  in  its  centre.  Columnai-  simple  epithelium  is  found 
covering  the  mucous  lining  of  the  stomach,  of  the  greater 
part  of  the  intestinal  canal,  and  of  the  ducts  of  many  secret- 
ing glands.  A  variety  of  this  epithelium,  with  shorter 
cubical,  prismatic  cells,  is  found  covering  the  mucous  lining 
of  the  smaller  bronchi,  of  the  ducts  of  certain  secreting 
cells,  and  of  portions  of  the  uriniferous  tubules.  Columnar 
and  cubical  simple  epithelial  cells  are  found  covering  the 
lining  of  the  respiratory  tract,  of  the  Fallopian  tubes,  and 
of  portions  of  the  genital  tract. 

(h)  Stratified  Epithelium. 
In  this  variety  numerous  layers  of  epithelial  cells  are 
superimposed  upon  the  basement  membrane;  of  these,  the 
basilar  layer  consists  generally  of  cylindrical,  the  middle 
layer  of  polygonal,  and  the  superficial  layers  of  squamous 
and  scaly  cells.  Stratified  epithelium  is  found  covering  the 
skin  and  the  mucous  membrane  of  the  mouth,  the  oeso- 
phagus, and  the  vagina. 

(c)  Transitional  Epithelium. 
In  this  variety  there  are  also  a  number  of  layers  of  cells 
superimposed  upon  the  basement  membrane,  but  in  such  a 
manner  that  the  outer  layer  consists  of  columnar,  the 
middle  layer  of  polyhedral,  and  the  basilar  layer  of  cubical 
cells.     Transitional  epithelium  is  found  covering  the  mu- 


THE   EPITHELIAL   TISSUES.  15 

■cous  lining  of  the  pelvis  of  the  kidneys,  of  the  ureters,  and 
of  the  bladder.  The  mucous  lining  of  the  vas  deferens  is 
also  covered  with  transitional  epithelial  cells,  but  here  the 
free  borders  of  the  outer  cells  present  cilia. 

(d)  Olandular  Epithelium. 

Glandular  epithelial  cells  are  those  which  possess  the 
property  of  secretion;  their  protoplasm  produces  materials 
which  fill  the  vacuoles  of  the  cell-body  and  are  finally  eli- 
minated. In  the  human  body  these  cells  are  found  scat- 
tered freely  between  the  cells  of  the  epithelial  lining  of  the 
intestinal  canal;  they  are  called  gohlet-cells  and  secrete  a 
tenacious  substance  called  mucin.  Secreting  cells  are  also 
found  covering  the  lining  of  certain  epithelial  involutions, 
called  secretiyig  glands. 

The  Structure  of  the  Secreting  Glands. — A  secreting 
gland  is,  as  has  been  stated,  a  more  or  less  complicated  in- 
volution of  epithelium. 

It  consists  of  a  basement  membrane  supporting  one  or 
more  layers  of  epithelial  ceUs.  A  secreting  gland  consists 
of  two  portions — viz.,  a  duct  and  a  secreting  portion.  The 
duct  is  lined  with  non-secreting  cubical  or  columnar  cells. 
The  gland  is  embedded  in  connective  tissue,  which  supports 
the  vessels  and  nerves  supplying  it.  The  secretory  activity 
of  the  gland  is  excited  by  a  stimulus  received  through  se- 
cretory nerve-fibres.  The  secreting  glands  are  divided,  ac- 
cording to  their  structure,  into: 

1.  Tuhidar:  (a)  simple,  (6)  compound. 

2.  Acinous  or  alveolar:  (a)  simple,  (6)  compound. 

Simple  tubular  secreting  glands  are  finger-like  depres- 
sions, lined,  in  their  upper  part  or  duct,  with  columnar  or 
cubical  cells,  and  in  their  lower  secreting  portion  with  glan- 
dular cells.  Examples  of  this  variety  are  found  in  the  mu- 
cous membrane  of  the  stomach,  small  intestines,  and 
uterus.  The  sudoriferous  glands  are  also  simple  tubular 
glands,  but  their  secreting  portion  is  generally  coiled. 


16       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

Compound  tubular  or  branching  tubular  glands  are 
those  in  Avhich  the  secreting  portion  consists  of  a  number 
of  tubules,  all  opening  into  one  common  duct.  Examples 
of  this  variety  are  the  gastric  and  intestinal  glands. 

Simple  acinous  or  alveolar  glands  are  those  in  which  the 
secreting  portion  of  a  pouch  like  expansion  is  called  the 
alveiis.  This  sometimes  has  numerous  recesses  which  open 
into  it ;  these  are  called  alveoli  Glands  thus  constructed 
are  called  compound  acinous  or  alveolar  glands:  they  pre- 
sent a  grape-like  appearance,  and  are,  for  this  reason,  also 
called  racemose  glands.  Examples  of  this  variety  are  the 
salivary,  the  mammary  glands,  and  the  pancreas. 


LECTURE  IT. 

II.     THE    CONNECTIVE    TISSUES. 

Having  completed  at  my  last  lecture  the  description  of 
the  epithelial  tissues,  their  wide  distribution  and  impor- 
tant physiological  functions,  I  will  to-day  take  up  the  con- 
nective tissues.  The  function  of  these  tissues  is  a  mechani- 
cal one;  they  hold  in  place  the  various  internal  organs, 
connect  and  support  the  various  elements  of  the  organs, 
and  form  the  skeleton,  ligaments,  tendons,  cartilages,  etc. 
The  connective  tissues  are  composed  of  an  intercellular 
substance,  which  may  be  fibrous,  homogeneous,  or  solid; 
embedded  in  this  are  the  cells,  also  called  connective-tissue 
corpuscles.     The  tissues  belonging  to  this  class  are: 

1.  White  fibrous  tissue. 

2.  Yellow  elastic  tissue. 

3.  Areolar  tissue. 

4.  Adipose  tissue. 

5.  Adenoid  tissue. 
C.  Cartilage. 

7.  Bone  tissue. 

8.  Dentin,  enamel,  and  cementum. 

1.  White  fibrous  tissue  is  composed  of  an  intermediate 
substance  formed  of  fibrillse  about  j-ohru-  ^^  ^^  ii^ch  thick. 
These  are  arranged  longitudinally  in  bundles  and  are  held 
together  by  a  cementing  substance.  Between  the  bundles 
are  lodged  the  cells  called  fibroblasts  ;  these  are  nucle- 
ated, quadrangular  cells  arranged  in  rows.  The  tendons, 
aponeuroses,  periosteum,  perichondrium,  dura  mater,  and 

2 


18      LECTURES  ON   HUMAN  PHYSIOLOGY  AND   HISTOLOGY. 

the  sheaths  of  tendons  are    composed  of  white  fibrous 
tissue. 

2.  Yellow  elastic  tissue  Consists  also  of  a  fibrous 
intercellular  substance,  but  the  fibres  are  coarse,  being 
about  iniinr  of  an  inch  thick  and  highly  elastic;  when  cut 
they  curl  at  the  cut  ends;  seen  under  the  microscope  the 
fibres  are  colorless,  but  en  masse  they  give  to  the  tissues 
a  yellowish  color. 

The  fibres  interlace  and  form  bundles,  between  which 
flattened  cells  are  situated.  Certain  ligaments — for  in- 
stance, the  ligamentum  nuchae — are  composed  of  this  tis- 
sue. Yellow  elastic  fibres  are  also  contained  in  the  coats 
of  the  arteries,  in  the  lung  tissue,  in  the  vocal  cords,  and 
in  areolar  tissue. 

3.  Areolar  tissue  consists  of  fine  interlacing  fibres. 
These  together  form  a  network  in  the  meshes  of  which  are 
contained  the  cells;  these  are  branched  and  cemented  by 
their  processes.  This  tissue  is  very  widely  distributed  in 
the  body.  The  sheaths  of  muscles,  nerves,  vessels,  glands, 
and  the  basement  membrane  of  the  membranes  are  all 
composed  of  areolar  tissue.  The  tissue  sustaining  the  ele- 
ments of  the  internal  organs  is  also  areolar. 

4.  Adipose  tissue  consists  of  a  network  of  areolar  tissue 
holding  in  its  meshes  clusters  of  cells  of  about  -^  of  an 
inch  in  diameter;  these  cells  contain  liquid  fatty  matter. 
The  tissue  also  supports  blood-vessels  and  nerves.  Adipose 
or  fat  tissue  is  present  to  a  greater  or  less  degree  in  almost 
all  parts  of  the  body. 

The  purposes  and  functions  of  adipose  tissue  are  (a)  to 
serve  as  a  storehouse  for  combustible  matter  which  may 
be  used  by  the  tissues  when  required ;  (b)  to  act  as  a  pack- 
ing material,  thus  preventing  pressure  upon  delicate  struc- 
tures; (c)  to  prevent  an  undue  escape  of  heat  from  the 
surface  of  the  body,  since  the  adipose  tissue  contained 
beneath  the  skin  is  a  poor  conductor  of  heat. 

5.  Adenoid  tissue,  also  called  retiform  or  lymphoid  tis- 


THE    COXNECTIVE    TISSUES.  19 

-sue,  is  that  which  makes  up  the  stroma  of  the  spleen, 
tonsils,  lymphatic  glands,,  etc.  It  consists  of  a  fibrillar 
network  holding  in  its  meshes  the  so-called  lymphoid  cor- 
puscles; these  are  spherical  cells  with  large  nuclei. 

«;.  Cartilage.  This  tissue  consists  of  a  semi-solid,  dense 
intercellular  substance  called  the  matrix.  In  it  are  em- 
bedded the  cartilage  cells,  or  chondroblasts,  which  have 
various  forms  and  often  contain  glycogen.  Cartilage,  when 
boiled,  yields  a  gelatinous  substance  called  chondrin.  All 
cartilage,  except  that  covering  the  articular  surface  of  bone, 
is  covered  by  a  dense  fibrous  membrane,  called  the  jjeri- 
cho'iidrium,  which  closely  adheres  to  the  cartilage  and 
serves  for  its  nutrition.  The  function  of  cartilage  is  to  give 
strength  and  elasticity  :  it  is  therefore  found  in  the  body 
wherever  a  strong,  elastic,  yielding  substance  is  required — 
for  instance,  in  the  larynx  and  trachea,  where  it  serves  to 
keep  them  in  shape,  or  between  articular  siu'f aces  of  bones, 
where  it  prevents  jarring  of  the  body.  In  the  human 
I)ody  we  find  three  varieties  of  cartilage,  namely  :  (a)  hija.- 
line  cartilage,  (6)  yelloiv  elastic  cartilage,  (c)  ahite  fihrov.s 
<:artilage. 

{a)  Hyaline  cartilage  consists  of  a  matrix  composed  of  a 
homogeneous,  translucent  material,  and  containing  smaU 
cavities  called  lacunce.  In  these  are  embedded  from  four 
to  eight  irregular-shaped  cells,  each  of  which  has  a  nucleus 
and  a  nucleolus.  The  lacunae  are  lined  with  a  dehcate  mem- 
brane, and  are  connected  with  each  other  by  minute  chan- 
nels which  transmit  nutritive  material.  The  cartilages  of 
the  bronchi,  trachea,  nose,  some  of  those  of  the  larynx, 
and  the  articular  cartilages  of  the  joints,  are  of  this  variety. 
(b'  YeUov:  elastic  cartilage  consists  of  a  matrix  of  hya- 
line material  and  of  yellow  elastic  fibres;  the  cells  are  more 
round  than  those  of  the  hyahne  variety.  The  epiglottis, 
the  cornicula  laryngis,  the  cartilaginous  portion  of  the 
Eustachian  tube,  and  the  cartilages  of  the  auricle  of  the 
external  ear  are  of  this  varietv. 


20      LECTURES   ON   HUMAN    PHYSIOLOGY    AND    HISTOLOGY. 

(c)  White  Jibro-cartilage.  In  this  Yariety  the  matrix 
consists,  as  the  name  imphes,  of  a  fibrous  material.  The 
cells  are  flattened  and  sometimes  branching.  This  car- 
tilage is  Yeiy  abundant  in  the  human  body.  The  intra- 
articular cartilages  between  certain  joints ;  the  circum- 
ferential cartilages  attached  to  the  margin  of  certain  joint- 
caYities,  hke  the  glenoid,  the  acetabulum,  etc.;  the  con- 
necting cartilages  between  the  Ycrtebrge  ;  and,  lastly,  the 
so-called  sesamoid  cai'tilages  contained  in  the  sheaths  of 
certain  tendons — are  all  composed  of  white  fibro-cartilage. 

7.  Bone.  This  tissue  is  composed  of  earthy  and  animal 
matter.  The  former  consists  chiefly  of  calcium  phosphate 
and  constitutes  67  per  cent  of  the  bone  substance,  while 
33  per  cent  is  animal  matter.  A  bone  consists  of  a  com- 
pact e;^ternal  layer  and  a  spongy  or  cancellous  internal 
portion. 

.  TJie  structure  of  bone  tissue.  The  compact  and  can- 
cellous portions  of  bone  haYC  both  the  same  structure. 
Bone  tissue,  when  examined  under  the  microscope,  is  seen 
to  consist  of  numerous  openings,  around  which  are  ar- 
ranged concentric  rings  of  bone  tissue.  In  this  are  seen 
minute  canities,  which  are  connected  with  each  other  and 
with  the  central  opening  by  dehcate  channels.  Such  a 
circular  arrangement  of  bone  tissue  is  called  the  Haversian 
system,  after  CJoptou  Havers,  who  first  described  it.  The 
central  opening  in  each  ring  is  the  opening  of  a  Haversian 
canal.  The  bony  ring  around  this  is  called  the  lamella, 
the  minute  caYities  are  termed  lacunce,  and  the  channels 
connecting  these  with  each  other  and  with  the  central 
opening  are  the  canalicnli. 

The  HaYersian  canals  are  channels  running  parallel  with 
the  long  axis  of  the  bone.  In  their. course  they  branch  off, 
communicate  with  each  other,  and  issue  either  at  the  sur- 
face of  the  bone,  or  at  the  medullary  canal  by  the  minute 
openings  through  which  blood-Yessels  and  lymphatics  enter 
the  bone. 


THE   CONNECTIVE   TISSUES.  21 

The  lacunae  are  small,  oblong  cavities  and  contain  the 
bone-cells. 

The  bone- corpuscles  are  flattened,  nucleated  cells  with 
branches  which  project  into  the  canaliculi.  They  are  sur- 
rounded by  fluid  nutrient  matter,  which  is  conveyed  thither 
through  the  canaliculi.  The  bone-cells,  or  osteoblasts,  are 
the  bone-forming  cells.  The  space  between  the  concentric 
rings  of  bone-tissue  just  described  is  also  composed  of 
bone-tissue,  and  is  called  the  interstitial  lamella.  It  con- 
tains lacunae  and  canaliculi,  but  not  in  a  characteristic 
arrangement  as  in  the  Haversian  system.  The  long  bones 
present  an  external  ring  of  compact  bone -tissue,  called 
the  circumferential  lamella,  the  structure  of  which  is  the 
same  as  that  of  the  interstitial  lamella. 

Bone-tissue  receives  its  nutrition  through  the  periosteum 
and  through  the  marrow.  The  periosteum  is  a  dense, 
highly  vascular,  fibrous  membrane  which  closely  adheres  to 
the  outer  surface  of  the  bone,  and  from  which  blood-ves- 
sels pass  into  the  bone-substance. 

"  The  marrow  of  bone  is  of  two  kinds:  (a)  Yellow  marrow 
is  that  which  is  contained  in  the  central  canal  of  the  long 
bones;  it  is  composed  of  areolar  tissue  which  supports  fat- 
cells  and  blood-vessels  ;  from  the  latter  there  are  branches 
which  enter  the  bone-substance,  (c)  Red  marrow  is  that 
contained  in  the  spongy  bone-tissue;  it  is  very  vascular,  and 
chiefly  composed  of  marrow-cells  which  resemble  lymphoid 
corpuscles  ;  these  cells  are  sometimes  reddish,  and  are  be- 
lieved to  be  in  a  transitional  stage  from  marrow-cells  to 
red  blood-corpuscles.  Bone-tissue  is  developed  from  the 
osteoblasts. 

8.  Dentin,  Enamel,  and  Cementum.  These  are  the 
tissues  which  enter  into  the  construction  of  the  teeth.  A 
tooth  consists  of  a  crown,  a  neck,  and  one  or  more  roots. 
The  last  mentioned  are  those  portions  of  the  tooth  which 
are  contained  in  the  alveoli  of  the  alveolar  process  of  the 
jawbone.     The  interior  of  a  tooth  is  a  cavity,  which  gene- 


22      LECTURES   ON    HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

rally  takes  the  form  of  the  tooth.  This  contaiDS  the  pulp 
and  is  called  the  pulp-chamber.  The  apex  of  each  root  pre- 
sents an  opening,  the  foramen  dentium,  which  transmits  the 
structures  forming  the  pulp.  The  pulp  consists  of  blood- 
vessels and  nerve-filaments,  held  together  by  areolar  tissue. 
The  pulp  is  covered  by  a  single  layer  of  elongated  cells,  the 
odontoblasts;  these  are  connected  by  processes  with  the 
pulp,  and  also  project  elongated  processes  into  the  dentinal 
canals  of  the  dentin. 

The  dentin  is  one  of  the  hardest  tissues  in  the  human 
body.  It  consists  of  a  matrix  of  inorganic  material,  pierced 
by  numerous  slightly  curved  S-shaped  channels,  called  the 
dentinal  canals,  which  radiate  from  the  pulp-chamber 
toward  the  periphery  of  the  dentin,  where  they  open  into 
small  spaces  called  the  interglobular  spaces.  The  dentinal 
canals  are  lined  with  a  delicate  membrane,  called  the  deii- 
tinal  sheath.  These  canals  contain  the  dentinal  fibres,  which 
are  the  prolonged  processes  of  the  odontoblasts;  they  ter- 
minate at  the  periphery  of  the  dentin,  and  are  here  con- 
nected with  the  poles  of  the  branching  cells  contained  in  the 
interglobular  spaces.  The  dentin  forms  the  main  mass  of 
the  body  of  the  tooth:  it  has  the  shape  of  the  tooth  and 
surrounds  the  pulp.  The  dentin  of  the  crown  is  covered 
by  the  enamel,  that  of  the  root  or  roots  by  the  cementum. 

The  enamel  is  the  hardest  tissue  in  the  human  body.  It 
consists  of  prisms  composed  of  inorganic  material;  these 
are  set  at  right  angles  upon  the  surface  of  the  dentin, 
forming  the  crown  of  the  tooth.  Enamel  contains  only 
from  3  to  5  per  ce.nt  of  organic  material.  In  early  life  the 
enamel  is  covered  by  an  exceedingly  delicate  membrane, 
called  the  ctiticnla. 

The  cementum,  or  crusta  ptetrosa,  is  bony  tissue  which, 
in  a  thin  layer,  covers  the  dentin  of  the  roots  of  the  teeth. 
The  bone-cells  contained  in  its  lacunae  are  connected  by 
this  elongated  process  with  the  branched  cells  contained 
in  the  interglobular  spaces.     Externally  the  cementum  is 


THE   CONNECTIVE   TISSUES.  33 

covered  by  a  dense,  delicate  vascular  membrane,  which 
closely  adheres  to  the  cementum,  and  which  to  some  extent 
supplies  nutritive  material  to  the  tooth;  it  is  called  the 
pericementum  and  is  continuous  with  the  periosteum  lining 
the  alveoli. 

In  the  lectures  on  dental  histology  you  will  listen  to  a 
more  detailed  description  of  the  structure  of  the  teeth. 
On  their  functions  and  on  their  development  I  will  dwell 
in  future  lectures. 


LECTURE  V. 

In  my  last  lecture  I  finished  the  description  of  the  ele- 
mentary tissues.  To-day  I  shall  begin  that  of  the  higher 
speciahzed  tissues — viz.,  those  of  the  muscles  and  nerves. 
At  present  I  will  consider  the  histology  and  physiology  of 
these  tissues  only  so  far  as  it  is  essential  for  a  proper 
understanding  of  those  physiological  functions  of  which  I 
will  speak  in  the  next  series  of  lectures. 

In  my  lectures  on  animal  motion  and  on  the  physiology 
of  the  nervous  system  I  will  consider  these  tissues  more  in 
detail,  paying  especial  attention  to  their  physiology. 

III.    THE   MUSCULAR  TISSUES. 

In  the  human  body  we  find  three  varieties  of  this  tissue 
— the  plain  or  non-striated,  the  striated,  and  the  cardiac 
muscle. 

Plain  or  Non-striated  Muscle  Tissue. — This  variety  is 
found  in  the  coats  of  the  blood-vessels,  lymphatics,  ducts 
of  glands,  in  the  walls  of  the  gall-bladder,  urinary  bladder, 
ureters,  stomach,  intestines,  uterus,  trachea,  bronchi,  lower 
half  of  the  oesophagus,  also  in  the  eye  and  in  the  skin. 

The  Structure  of  Plain  or  Non-striated  Muscle  Tissue. — 
The  histological  elements  of  this  tissue  are  the  contrac- 
tile fibre-cells.  These  are  elongated,  flat,  spindle  shaped, 
nucleated  cells  which  are  from  ^f^  to  -^  and  even  to  -jV 
of  an  inch  long,  and  -^-^^  to  g-gVo  of  an  inch  wide  at  their 
widest  part.  These  cells  have  an  elastic  limiting  mem- 
brane. The  cell-body  consists  of  longitudinally  arranged 
fibrillse,  which  are  the  real  contractile  elements  of  the  cell. 
The  elongated  nucleus  has  a  limiting  membrane  and  a 


THE   MUSCULAR   TISSUES.  25 

stroma  of  longitudinally  arranged  fibrillge,  which,  at  the 
poles  of  the  nucleus,  anastomose  with  the  fibrillar  of  the 
cell-body.  These  cells  are  held  together  by  a  cementing 
material  and  by  connective  tissue. 

Striated  Muscle  Tissue. — This  variety  forms  the  mus- 
cles of  the  skeleton.  The  structure  of  this  tissue  is  more 
complicated  than  that  of  the  former  variety.  Striated 
muscle  tissue  consists  of  fibres  which  are  from  one-half  to 
two  inches  long  and  g^  to  3-^  of  an  inch  in  diameter. 
These  fibres  are  surrounded  by  a  delicate  sheath,  the  sarco- 
lemma.  Examined  under  the  microscope  the  fibres  present 
alternating  dark  and  light  lines;  these  run  transversely, 
being  ytot  of  an  inch  in  width.  The  dark  lines  present 
minute  longitudinal  striae,  which  divide  each  into  a  row  of 
quadrangular  particles,  called  sarcous  elements.  The  light 
lines  are  divided  into  halves  by  a  transverse  dark  streak; 
this  is  formed  by  a  delicate  membrane,  called  Krause''s 
membrane,  which  passes  from  one  side  of  the  sarcolemma 
to  the  other.  This  membrane  divides  the  inside  of  the 
muscular  fibre  into  compartments,  called  discs  of  Boivman. 
Each  compartment  consists  of  a  row  of  sarcous  elements 
forming  a  dark  line,  and  a  translucent  cementing  material 
which  holds  the  sarcous  elements  together  ;  this  substance 
forms  the  delicate  longitudinal  striae  in  the  dark  lines,  and 
the  portions  of  the  light  lines  which  are  between  the  dark 
line  and  Krause's  membranes.  A  continuous  connective 
tissue  holds  the  individual  fibres  in  bundles.  A  number  of 
these  together  form  fasciculi  ;  a  group  of  fasciculi  forms  a 
'  muscle,  which  is  surrounded  by  a  sheath.  The  connective 
,tissue  holding  together  the  fibres  in  bundles  is  called  endo- 
mysium;  that  holding  the  bundles  together,  the  internal 
perimysium;  and  that  holding  the  fasciculi  together  to  form 
and  surround  a  muscle  is  called  the  external  perimysium. 

The  Cardiac  Muscle  Tissue. — This  variety  is,  as  the  iiame 
implies,  the  tissue  which  forms  the  heart  muscle.  Its 
.structure  resembles  that  of  the  striated  variety,  in  that  it 


26      LECTURES   OX   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

is  also  made  up  of  fibres  ^vhich  have  a  striated  appearance. 
The  fibres  are  only  about  one-third  the  size  of  those  of  the 
voluntary  muscles.  They  have  no  sarcolemma,  and  their 
transverse  and  longitudinal  striae  are  less  distinct.  The 
fibres  consist  of  oblong,  nucleated  prisms,  and  branch  off 
and  anastomose  with  each  other  ;  the  connective  tissue 
holding  them  together  is  less  abundant  than  in  the  former 
variety. 

The  physiological  property  of  muscle  tissue  is  its  con- 
tractility. This  is  an  inherent  property,  as  shown  by  the 
fact  that  it  will  also  exert  this  activity,  under  certain  con- 
ditions, when  all  nervous  connections  with  the  muscles  are 
severed.  The  activity  of  muscle  tissue  is  generally  excited 
by  stimuli  received  through  nerves.  The  activity  of  the 
skeleton  muscles  is  under  the  control  of  the  will,  and  these 
muscles  are  for  that  reason  called  voluntary  muscles;  where- 
as the  activity  of  the  non- striated  and  the  cardiac  muscle 
tissue  is  not  under  the  control  of  the  will,  and  they  are- 
therefore  called  involuntary  muscles. 

IV.    THE   NERVE-TISSUE. 

The  histological  and  physiological  elements  which  enter 
into  the  structure  of  the  nerve-tissue  are  :  (a)  nerve-cells, 
(6)  nerve-fibres,  and  (c)  connective  tissue.  The  peripheral 
termini,  which  also  are  portions  of  the  nervous  system,  pos- 
sessing a  special  structure,  wall  be  described  in  my  lectures 
on  the  physiology  of  the  nervous  system. 

(a)  Structure  and  Functions  of  the  Nerve- Cells. -—^QvyQ- 
cells,  nerve-vesicles,  or  ganglionic  cells  vary  in  size  from 
■^  to  yV  c>f  ^  millimetre  in  diameter.  They  are  either  an- 
gular, oval,  or  stellate  in  form,  and  generally  have  one 
or  more  protoplasmic  processes,  called  poles ;  accordingly 
nerve-cells  are  said  to  be  unipolar,  bipolar,  tripolar,  or 
multipolar.  These  poles  either  terminate  in  a  point,  or 
anastomose  w^ith  the  poles  of  other  nerve-cells,  or  continue 
as  the  axis-cylinder  of  a  nerve-fibre.  Nerve-cells  have  no 
distinct  cell- wall,  but  a  clear  round  or  oval  nucleus  w4th 


THE   NERVE-TISSUE.  27 

an  intranuclear  network  and  generally  a  nucleolus.  The 
cell-body  is  composed  of  a  reddish  granular  protoplasm. 
Nerve-cells  are  the  chief  structure  of  the  nerve-centres. 

The  physiological  functions  of  the  nerve  cells  may  be 
enumerated  under  the  following  heads:  Conduction,  reflec- 
tion, transference,  automaticity,  augmentation,  and  inhibi- 
tion. Conduction  is  the  property  possessed  by  certain 
nerve-cells  enabling  them  to  conduct  impressions  to  other 
nerve-cells  or  centres.  Reflection  is  the  property  by  which 
certain  nerve-cells  transmit  to  the  periphery  impulses  re- 
ceived through  nerves  coming  from  the  periphery.  Trans- 
ference is  the  property  by  which  certain  nerve-cells  inter- 
posed in  the  course  of  nerves  or  nerve-fibres  transfer 
impulses  from  one  nerve  fibre  to  another.  Automaticity 
is  the  property  enabling  certain  nerve-cells  to  originate 
impulses  without  external  stimuli.  Augmentation  is  the 
property  of  augmenting,  altering,  or  influencing  the  kind 
and  quality  of  certain  nerve  impulses.  Inhibition  is  the 
property  which  certain  nerve-cells  possess  enabling  them 
to  inhibit  the  activity  of  others. 

In  my  lectures  on  the  physiology  of  the  nervous  system 
I  will  more  fully  explain  and  illustrate  these  functions  of 
the  nerve-cells. 

(6)  Structure  and  Functions  of  the  Nerve-Fibres. — Nerve- 
fibres  are  the  chief  structures  entering  into  the  formation 
of  the  nerves.  Nerve-fibres  are  either  medullated  or  non- 
meduUated.  A  medullated  nerve-fibre  consists  of:  (a)  The 
axis-cylinder.  This  is  the  essential  portion  of  all  nerve- 
fibres  ;  it  is  of  a  reddish- gray  color,  consists  of  deUcate 
fibrillse,  and  is,  as  the  name  implies,  the  central  portion  of 
the  nerve-fibre.  The  axis-cylinder  passes  uninterruptedly 
from  origiii  to  end ;  its  physiological  function  is  to  con- 
vey impulses  or  impressions  either  to  or  from  the  centre. 
{b)  The  medullary  sheath,  also  called  the  white  substance 
of  Schioann,  or  myeline  sheath,  is  a  semi-solid,  whitish,  fatty 
substance  surrounding  the  axis-cylinder ;  its  thickness 
varies.     The  function  of  the  medullary  sheath  is  to  serve 


28      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

as  an  isolatiog  material.  Non-medullated  nerve-fibres  are 
not  surrounded  by  this  medullary  sheath,  (c)  The  comiective 
tissue.  Tissue  of  this  variety  enters  into  the  structure  of 
the  nerve-tissue;  it  serves  to  hold  its  various  structures  to- 
gether. 

Neurilemma  is  a  delicate  fibrous  membrane  which  sur- 
rounds certain  nerve-fibres.  In  this  delicate  tubular  sheath 
are  seen  at  intervals  large,  oval  nuclei  surrounded  by  pro- 
toplasmic masses;  these  are  called  nerve-corpuscles,  and 
they  are  believed  to  be  remnants  of  an  embryonic  life.  At 
intervals  the  neurilemma  of  many  medullated  nerve-fibres 
presents  constrictions  by  which  the  continuance  of  the  me- 
dullary sheath  is  interrupted,  because  of  which  the  nerve- 
fibres  present  a  nodulated  appearance  The  nodules  are 
called  nodes  of  Ranvier.  Not  all  nerve-fibres  have  a  neuri- 
lemma. Endoneurium  is  the  connective  tissue  which  holds 
in  a  bundle  a  number  of  individual  nerve-fibres.  Perineu- 
rium is  the  connective  tissue  which  holds  together  the 
bundles  forming  a  nerve-trunk.  The  epine^irium  is  the 
connective  tissue  which  forms  the  sheath  of  a  nerve-trunk. 
The  neuroglia  is  a  special  form  of  connective  tissue  which 
supports  and  holds  together  the  elements  of  the  brain  and 
spinal  cord.  It  consists  of  a  homogeneous,  fatty,  whitish 
substance  which  contains  delicate  fibriUse  holding  in  their 
meshes  nucleated  cells. 

This  finishes  the  description  of  the  structures  forming 
the  nervous  system,  and  I  repeat  that  it  is  merely  intro- 
ductory to  your  practical  work  in  histology  and  to  your 
studies  of  the  physiology  of  the  nervous  system. 

With  this  lecture  I  also  finish  the  description  of  the  tis- 
sues, as  far  as  I  intend  to  treat  of  them  in  this  series  of  lec- 
tures, which  are  really  only  preliminary  and  introductory 
to  the  subject  of  physiology.  The  tissues  mentioned  in 
the  classification  under  No.  5 — namely,  the  fluid  tissues — 
are  the  blood,  the  lymph,  and  the  chyle.  These  are  fluids 
consisting  of  cells  and  a  fluid  intermediate  substance,  hence 
the  name  fluid  tissues.    The  lymph  and  the  chyle  I  will 


QUESTIONS  AND   EXERCISES.  '  35 

describe  when  speaking  of  the  subjects  of  digestion  and  ab- 
sorption.    The  subject  of  my  next  lecture  will  be  the  blood. 


QUESTIONS   AND   EXERCISES. 

Subject. — Terminology.  Definitions.  The  cell;  the  cell 
theory ;  cell  multiplication.  The  tissues;  their  struc- 
ture, function,  and  distribution. 

Lectures  I.- V.  inclusive. 

1.  What  is  physiology  ? 

2.  What  is  biology  ? 

3.  What  is  morphology  ? 

4.  What  is  histology  ? 

5.  What  is  embryology  ? 

6.  What  is  a  cell  ? 

7.  What  is  the  first  description  of  the  animal  cell  ? 

8.  What  is  the  essential  part  of  a  cell  ? 

9.  What  is  protoplasm  ? 

10.  What  is  a  cell- wall  ? 

11.  What  is  a  cell-nucleus  ? 

12.  Describe  the  minute  structure  of  the  cell-body. 

13.  Describe  the  minute  structure  of  the  cell-nucleus. 

14.  What   is   a  chromatic  and   what  is   an   achromatic 
substance  ? 

15.  What  are  the  chemical  constituents  of  protoplasm  ? 

16.  What  are  the  properties  of  protoplasm  ? 

17.  How  do  cells  originate  ? 

18.  How  do  the  cells   of  the  higher  animal  organism 
generally  multiply  ? 

19.  Describe  the  process  of  indirect  cell  division: 

(a)  The  changes  taking  place  in  the  chromatic 

substance  of  the  nucleus. 
(6)  The  chaDges  taking  place  in   the  achromatic 

substance. 
/  (c)  Those  of  the  cell-body. 


30      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

20.  Describe  the  various  forms  of  cells  found  in  the 
tissues  of  the  human  body. 

21.  Describe  the  special  functions  of  the  various  cells  of 
the  tissues. 

22.  What  is  a  tissue  ? 

23.  Name  the  varieties  of  epithelial  tissues. 

24.  Describe  the  structure,  the  functions,  and  the  distri- 
bution of  (a)  simple,  (6)  transitional,  and  (c)  stratified 
epithelium. 

25.  Describe  the  various  forms  of  secreting  glands,  and 
naine  examples  of  each. 

26.  Name  the  connective  tissues. 

27.  Describe  the  structure  of  white  fibrous  tissue  and  its 
distribution. 

2S.  Describe  the  structure  of  yellow  elastic  tissue  and  its 
distribution. 

29.  Describe  the  structure  and  distribution  of  (a)  areolar, 
(6)  adenoid,  and  (c)  adipose  tissue. 

30.  Describe  the  varieties  of  cartilage,  their  structure 
and  distribution. 

31.  Describe  the  structure  of  bone-tissue. 

32.  Describe  the  structures  which  enter  into  the  con- 
struction of  a  tooth. 

33.  What  are  odontoblast,  dentinal  fibres,  dentinal  sheath? 

34.  What  is  the  physiological  function  of  muscle-tissue  ? 

35.  Name  the  varieties  of  muscle-tissue. 

36.  Describe  the  structure  of  non-striated  muscle. 

37.  Describe  a  striated  muscular  fibre. 

38.  Describe  the  structure  of  cardiac  muscle. 

39.  Define  external  perimysium,  internal  perimysium, 
endomysium,  sarcolemma. 

40.  Name  the  structural  elements  which  enter  into  the 
construction  of  the  organs  of  the  nervous  system. 

41.  Describe  the  structure  of  a  nerve-cell. 

42.  Explain  the  physiological  functions  of  a  nerve-cell. 

43.  Describe  the  structure  of  a  meduUated  nerve-fibre. 


QUESTIONS   AND   EXERCISES.  31 

44.  Explain  the  difference  between  a  medullated.  and 
non-medullated  nerve-fibre. 

45.  Explain  the  physiological  functions  of  nerve-fibres. 

46.  Define  neurilemma,  endoneurium,  perineurium,  epi- 
neurium. 

47.  What  is  neurogUa  ?    Describe  its  structure. 

48.  What  are  the  fluid  tissues  ? 

49.  What  variety  of  membrane,  serous  or  mucous,  lines 
the  inside  of  each  of  the  following:  abdominal  cavity,  ali- 
mentary canal,  thoracic  cavity,  nasal  passages,  eyelids  ? 

50.  What  is  the  function  of  adipose  tissue  ? 

51.  Describe  the  structure  of  muscle. 

52.  Describe  the  structure  of  a  tooth. 

53.  Describe  the  development  of  the  nuclei  of  cells. 

54.  Define  the  function  of  the  mucous  membrane  of  the 
respiratory  tract. 

55.  To  what  class  of  tissues  do  teeth  belong  ? 

56.  Define  tissue. 

57.  Describe  a  nerve-fibre. 

58.  What  is  the  function  of  the  serous  and  the  synovial 
membranes  ? 

59.  Give  the  functions  and  localities  of  each  of  the  differ- 
ent varieties  of  epithelia. 

60.  Describe  an  amoeba. 

61.  What  is  the  function  of  the  Schneiderian  mem- 
brane ? 

62.  How  are  cells  reproduced  ? 

63.  Describe  ciliary  motion. 

64.  Describe  protoplasmic  movement. 

65.  Describe  the  decay  and  death  of  cells. 

66.  How  are  cells  connected  ? 

67.  Name  the  physical  properties  of  protoplasm. 

68.  Draw  a  cell,  designating  three  parts  of  it. 


LECTUEE   YI. 

THE   PHYSIOLOGY   OF   THE   BLOOD. 

All  living  organisms  receive  their  nutrition  from  a  juice 
which  permeates  all  parts.  In  the  lower  forms  of  animal 
life  this  juice  is  either  colorless  or  somewhat  yellow.  In 
higher  forms  it  is  red  and  is  called  the  blood;  it  circulates 
in  a  closed  system  of  vessels  which  are  distributed  to  all 
parts  of  the  body. 

Human  blood  is  an  opaque  fluid.  For  a  proper  under- 
standing of  its  physiology  it  is  necessary  to  describe  and 
explain  its  physical  properties,  such  as  its  color,  specific 
gravity,  reaction,  odor,  taste,  etc.,  before  describing  its 
morphological  constituents. 

The  color  of  human  blood  varies  from  scarlet  or  dark-red 
to  purple.  The  color  of  the  blood  is  due  to  a  coloring 
material  contained  in  the  red  blood-corpuscles;  this  is  called 
hcemoglobin.  It  forms  with  oxygen  a  bright-red  compound; 
the  combination  is  an  unstable  one,  and  the  oxygen  is  eas- 
ily given  off  again  when  pressure  is  removed.  The  haemo- 
globin thus  reduced  has  a  dark-red  color.  This  explains 
the  difference  between  the  color  of  the  blood  in  the  arteries 
and  capillaries  and  that  in  the  veins. 

The  specific  gravity  of  human  blood  varies  from  1045  to 
1055;  it  is  generally  higher  in  man  than  in  woman.  The 
specific  gravity  of  blood  is  dependent  upon  the  quantity  of 
hcemoglobin  in  the  blood,  and  also  upon  the  comparative 
quantity  of  water. 

Fasting,  or  any  condition  in  which  large  quantities  of 
liquid  are  taken,  decreases  the  specific  gravity  of  the  blood 


THE   PHYSIOLO(?Y   OF   THE   BLOOD.  53 

whereas  any  condition  in  which  large  quantities  of  water 
are  given  off  through  the  skin,  intestines,  or  kidneys  in- 
€reases  it. 

Pathological  conditions  which  influence  the  quantity  of 
red  blood-corpuscles  or  of  their  haemoglobin  also  influence 
the  specific  gravity.  It  is  for  this  reason  that  in  anaemia, 
chlorosis,  nephritis,  and  in  marasmatic  conditions  the  spe- 
cific gravity  of  the  blood  is  lowered. 

The  reaction  of  human  blood  is  shghtly  alkaline,  due  to 
the  presence  of  alkaline  salts  in  the  blood.  The  alkaUnity 
of  the  blood  is  generally  greater  in  men  than  in  women  and 
children.  When  blood  is  taken  from  the  circulatory  sys- 
tem it  soon  loses  its  alkalinity  ;  this  is  believed  to  be  due 
to  an  acid  which  forms  during  the  decomposition  of  the 
haemoglobin.  Muscular  exercise,  the  taking  of  acids,  and 
fasting  decrease,  and  the  reverse  conditions  increase,  the 
alkalinity  of  the  blood.  Many  pathological  conditions  also 
influence  the  alkalinity,  which  is  increased  in  chlorosis  and 
in  diseases  of  which  excessive  vomiting  is  a  symptom  ;  a 
marked  decrease  of  the  alkalinity  of  the  blood  is  observed  in 
anaemia,  uraemia,  rheumatism,  gout,  cholera,  and  in  febrile 
conditions.  The  same  result  takes  place  when  poisonous 
substances  are  taken  which  destroy  the  red  blood-corpus- 
cles. 

It  is  of  great  importance  for  the  clinician  to  be  able  to 
determine  the  relative  alkalinity  of  the  blood.  The  process 
used  for  this  purpose  is  as  follows  :  A  weak  solution  of  tar- 
taric acid  (Y.5  to  1000.0)  is  prepared;  a  sufficient  amount  of 
this  is  added  to  a  given  volume  of  blood  to  render  it  neutral, 
as  shown  by  the  use  of  litmus  paper.  A  test  with  this 
solution  will  demonstrate  that  1  cubic  centimetre  neutral- 
izes 0.0031  of  sodium.  Knowing  this,  and  knowing  the 
quantity  of  the  stated  solution  which  is  required  to  neu- 
tralize a  given  volume  of  blood,  it  is  but  a  simple  matter 
to  calculate  from  this  the  relative  alkalinity  of  that  vol- 
ume of  blood  :  100  cubic  centimetres  of  normal  human 
3 


34      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

blood  have  an  alkalinity  representing  0,20()  to  0.300  gramme 
of  sodium. 

The  odor  of  human  blood  is  a  characteristic  one,  due  to 
the  presence  of  certain  volatile  fatty  acids. 

The  taste  of  human  blood  is  saline  and  is  caused  by  the 
presence  of  salts,  especially  of  sodium,  chloride. 

To  the  touch  blood  is  warm  and  sticky. 

The  morphological  elements  of  the  blood  are  : 

1,  The  cells — viz.,  (a)  the  red  blood-corpuscles,  (b)  the 
white  blood-corpuscles,  (c)  the  blood-plates  or  blood-plaques 
(of  late  considerable  importance  has  been  attributed  to 
these). 

2.  The  plasma,  or  liquor  sanguinis,  which  is  the  inter- 
cellular substance. 

The  blood,  therefore,  like  the  lymph  and  chyle,  is  a  fluid 
tissue  consisting  of  cells  and  an  intercellular  substance. 
In  describing  its  morphological  elements  I  will  first  take 
up  the  corpuscles  and  then  the  plasma,  and  describe  the 
composition,  physical,  chemical,  and  physiological  proper- 
ties of  each,  and  then  dwell  on  the  physiology  of  the  blood 
in  general. 

I.    THE   BLOOD-CORPUSCLES. 

A.  TJie  Red  Blood-  Corpuscles  or  Erythrocytes.  — These  are 
cellular  elements  which  float  in  great  numbers  in  the 
blood.  In  the  human  blood  they  were  first  observed  by 
Van  Leeuwenhoeck  in  1673. 

A  human  red  blood-corpuscle  is  a  circular  disc  with  a 
central  depression  in  each  flat  surface,  so  that,  seen  from 
the  side,  it  is  biscuit-  or  dumbbell  shaped.  Erythrocytes 
have  no  cell-wall  and  no  nucleus  ;  their  body  is  composed 
of  a  homogeneous  gelatinous  protoplasm  and  is  very  elas- 
tic. A  human  red  blood-corpuscle  is  about  y|-^  of  a  milli- 
metre in  diameter,  ^  f?  of  ^  millimetre  thick  at  the'  edges, 
and  j-^  of  a  millimetre  thick  at  the  thinnest  portions. 
Human  red  blood-corpuscles  when  taken  from  fresh  blood 
can  be  recognized  as  such  by  their  form  and  size. 


THE   PHYSIOLOGY   OF   THE  BLOOD.  35 

All  mammalia  have  disc-like  erythrocytes,  \vith  the  ex- 
ception of  the  camel,  the  llama,  and  other  members  of  that 
family,  which  have  elliptical  red  blood-corpuscles.  The 
birds,  reptiles,  amphibiae,  and  fishes  have  oval  or  elliptical 
erythrocytes  which  contain  a  large,  protruding  nucleus. 

In  all  cases  where  the  red  blood-corpuscles  of  mammalia 
are  circular  and  disc  like  they  are  smaller  than  those  found 
in  human  blood,  with  the  exception  of  those  of  the  ele- 
phant, which  are  larger,  and  those  of  the  ape,  which  are 
but  slightly  smaller  than  those  of  human  blood. 

When  seen  under  the  microscope  red  blood-corpuscles 
are  straw-colored.  If  blood  is  examined  microscopically  it 
can  be  seen  that  the  red  blood-corpuscles  have  a  tendency 
to  cling  together  with  their  flat  surfaces,  thus  forming  pil- 
lars resembling  rolls  of  coins.  This  phenomenon  is  not  fully 
explained,  but  it  is  probably  due  to  changes  in  the  corpus- 
cles. In  circulating  blood  and  in  that  stagnant  in  the  blood- 
vessels this  tendency  has  not  been  observed. 

When  red  blood-corpuscles  are  kept  for  a  time  changes 
in  their  form  can  soon  be  observed  :  they  either  diminish  in 
size  and  assume  a  mulberry-shape,  caused  by  the  giving  off 
of  water,  or  swell  and  become  rounded  on  the  addition  of 
water  which  is  taken  up  by  the  corpuscles.  Liquids  used 
to  preserve  red  blood-corpuscles  are  :  a  physiological  solu- 
tion (0.6  per  cent)  of  sodium  chloride,  a  1  per  cent  solution 
of  egg-albumen,  and  Pacini's  fluid.  The  latter  is  composed 
of  hydrarg.  bichlor.,  2  parts;  natr.  chlorat.,  4  parts ;  gly- 
cerin, 26  parts;  aq.  destillat.,  226  parts.  For  use  this  solu- 
tion is  diluted  with  two  parts  of  distilled  water. 

Red  blood-corpuscles  are  composed  of  two  substances^ 
viz.,  the  hcemoglobin  and  the  stroma. 

The  chemical  composition  of  red  blood-corpuscles  is  as 
follows:  w-ater,  681  in  1,000  parts;  solids,  319  parts  (inor- 
ganic solids,  7  ;  organic  solids,  312).  The  inorganic  con- 
stituents are  the  salts  of  potassium,  sodium,  phosphorus, 


36      LECTURES    ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

and  magnesium.  The  organic  constituents  are  haemo- 
globin, albumin,  lecithin,  cholesterin. 

The  lioemoglohin  is  the  coloring  matter  of  the  red  blood- 
corpuscles.  It  is  a  nitrogenized,  organic,  crystallizable  sub- 
stance, composed  of  oxygen,  hydrogen,  nitrogen,  carbon, 
sulphur,  and  iron.  HO  is  the  symbol  used  for  the  word 
haemoglobin.  HO  can  be  obtained  from  the  blood  by  va- 
rious processes  in  the  form  of  rhombic  plates  and  prisms. 
It  is  soluble  in  water,  but  insoluble  in  alcohol,  chloroform, 
ether,  and  fats. 

The  quantity  of  HO  in  the  total  quantity  of  blood  is  in 
men  13.77  per  cent;  in  women,  12.59  per  cent;  during  preg- 
nancy only  9  to  12  per  cent.  It  is  highest  in  the  new-born, 
diminishes  after  the  tenth  week,  reaches  the  minimum  be- 
tween the  first  and  fifth  years,  then  gradually  increases, 
and  after  the  forty-fifth  year  decreases  again. 

In  certain  pathological  conditions  the  quantity  of  HO 
decreases — for  instance,  in  anaemia,  chlorosis,  in  all  febrile 
and  chronic  diseases,  and  in  marasmatic  conditions.  It  is, 
therefore,  of  great  importance  to  the  clinician  to  determine 
the  quantity  of  HO  in  the  blood.  This  can  be  determined 
with  the  use  of  the  haemameter  and  also  with  the  spectro- 
scope. Another  method  is  to  determine  the  quantity  of 
iron  in  the  blood,  from  which  the  quantity  of  HO  can  be 
calculated.     HO  contains  0.42  per  cent  of  iron  by  weight. 

HO  consists  of  two  substances,  viz.,  the  hcematin  and  an 
albuminous,  colorless  substance  belonging  to  the  class  of 
globulins. 

Hcematin  is  an  amorphous,  dark-blue  or  brownish  sub- 
stance containing  iron;  it  is  not  soluble  in  water,  alcohol, 
or  ether.  When  dried  HO  is  treated  with  glacial  acetic 
acid  and  sodium  chloride,  and  heat  is  applied,  minute 
crystals  are  produced  which  are  dark-blue  or  brown  and 
have  the  form  of  rhombic  plates  or  prisms.  These  are 
haematin  crystals,  composed  of  one  part  of  haematin  to 
two  of  HCl.     It  can  be  produced  from  the  smallest  parti- 


THE   PHYSIOLOGY   OF   THE   BLOOD.  37 

cles  of  dried  blood-stains,  and  is  for  this  reason  of  great 
importance  in  forensic  medicine,  especially  so  because  the 
form  of  the  crystals  is  characteristic. 

HO,  under  certain  conditions,  enters  into  chemical  com- 
bination with  gases  in  the  body.  We  find  in  the  body  the 
following  HO  combinations:  oxyhsemoglobin,  methsemo- 
globin,  and  CO  haemoglobin;  a  fourth  substance,  also  a  re- 
sult of  chemical  changes  of  HO,  is  the  ha?matoidin,  which 
is  found  in  the  body  under  certain  conditions.  Oxyhae- 
moglobin  (OHO)  forms  readily  when  HO  comes  in  contact 
with  0  or  with  air.  OHO  is  less  soluble  than  HO  and  dif- 
fers from  it  in  the  bands  of  the  spectrum.  OHO  is  found 
in  the  erythrocytes  of  the  blood  in  the  arteries  and  capil- 
laries. It  is  a  very  loose  chemical  compound,  and  readily 
gives  off  its  0  to  the  tissues  of  the  body;  it  is  then  called 
reduced  HO. 

Methcemoglobin — MetHO — is  a  more  stable  compound  of 
HO  with  0;  it  is  spontaneously  formed  in  bloody  urine,  cysts 
with  bloody  contents,  and  in  old  blood  extravasations.  It 
differs  from  OHO  in  the  arrangement  of  the  bands  in  the 
spectrum. 

Carbonic  o£C^(ie— HO(CO-HO) — is  a  chemical  compound 
which  is  readily  formed  when  CO  comes  in  contact  with 
OHO  or  HO.  It  is  cherry-red,  and  when  heated  with  a  ten 
per  cent  sodium  hydrate  solution  gives  a  bright- red  color. 
CO-HO  is  formed  in  the  body  when  CO  is  inhaled.  One 
volume  of  CO  replaces  one  volume  of  0  in  HO. 

CO  poisoning  occurs  when  sufficient  CO  is  inhaled  to  de- 
crease the  quantity  of  0  in  the  blood  to  such  an  extent  as 
to  interfere  with  the  vital  functions  of  the  tissues  depend- 
ing upon  a  proper  oxidation.  Death  occurs  before  all  0  is 
replaced  by  CO. 

The  symptoms  of  CO  poisoning  are :  headache,  rest- 
lessness, increased  cardiac  action,  rapid  circulation,  convul- 
sions; later  on,  loss  of  consciousness,  difficult  respiration, 
rapid  small  pulse  ;  and,  finally,  loss  of  sensation,  cesea- 


38      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

tion  of  cardiac  and  respiratory  action,  death.  The  blood- 
A^essels  are  first  contracted,  then  dilated,  the  organs  being 
congested  and  filled  with  cherry -red  blood.  One  thousand 
cubic  centimetres  of  CO  breathed  at  one  time  produce 
death.  Patients  suffering  from  CO  poisoning  should  be  re- 
moved into  the  fresh  air  and  artificial  respiration  and  stimu- 
lation resorted  to;  in  advanced  cases  transfusion  of  blood  is 
required.  CO-HO  is  also  formed  in  the  blood  when  minor 
quantities  of  CO  have  been  inhaled  with  the  air,  but 
through  the  respiratory  process  the  CO  is  gradually  re- 
placed by  oxygen. 

Hcematoiclin  is  another  substance  which  is  formed  in  the 
body  by  a  chemical  change  of  HO.  It  is  found  in  old 
extravasations  of  blood  in  the  brain.  It  is  always  found  in 
the  Graafian  follicle  after  its  rupture  during  the  mensk'ual 
period.  Haematoidin  is  formed  from  HO  when  the  latter 
gives  off  iron  and  takes  up  water;  it  is  bright  red  and  crys- 
tallizes in  klinorhombic  stars,  prisms,  and  plates. 

The  number  of  red  blood-corpuscles  has  been  estimated 
to  be  about  four  to  five  millions  in  one  cubic  millimetre  of 
blood;  generally  it  is  over  five  millions  in  men  and  about 
four  millions  in  women.  It  is  increased  after  the  taking  of 
solid  food  and  when  large  quantities  of  water  are  given  off 
through  the  skin,  kidneys,  or  intestines.  It  is  decreased 
after  the  taking  of  large  quantities  of  fiuid.  In  women  it 
is  generally  decreased  during  pregnancy.  Variations  in 
the  blood-pressure,  and  many  pathological  conditions,  such 
as  hydrfemia,  anaemia,  etc.,  influence  the  absolute  and  rela- 
tive quantity  of  erythrocytes  in  the  blood.  It  is,  therefore, 
of  no  little  importance  that  the  clinician  be  able  to  deter- 
mine such  variations.  The  apparatus  generally  used  for 
that  purpose  is  the  Abbe-Zeiss  counting  apparatus.  This 
consists  of  a  mixing  pipette  and  a  counting  chamber.  The 
mixing  pipette  consists  of  a  capillary  glass  tube,  at  the 
upper  portion  of  which  is  a  bulbous  expansion,  and  within 
this  a  glass  pearl  serving  to  thoroughly  mix  the  fluids 


THE   PHYSIOLOGY   OF   THE   BLOOD.  39 

drawn  up  into  it.  The  lower  end  of  the  tube  is  pointed; 
to  the  end  above  the  bulbous  expansion  a  rubber  tube  may 
be  attached  through  which  the  fluids  are  drawn  up  into  the 
tube  bulb.  The  pipette  has  engraved  on  it  the  figures  i, 
1,  and  100.  The  bulbous  expansion  is  between  the  marks 
1  and  100;  it  holds  one  hundred  times  more  than  the  capil- 
lary tube  from  the  point  to  the  mark  1,  and  two  hundred 
times  more  than  the  capillary  tube  from  the  point  to  the 
mark  ^. 

The  counting  chamber  consists  of  a  glass  cell  -jL  of  a  milli- 
metre deep;  this  is  fastened  upon  an  object  glass;  the  floor 
of  the  cell  is  divided  into  squares  of  ^j^  of  a  quadratmilli- 
metre  each.  The  cubic  contents  of  the  space  above  each 
of  these  little  squares  of  the  counting  chamber  is  therefore 
^-jjViT  of  a  cubic  millimetre. 

The  method  of  counting  the  red  blood-corpuscles  with 
the  use  of  this  apparatus  is  as  follows:  First,  the  blood  is 
diluted  with  200  or  100  volumes  of  a  physiological  (0.6  per 
cent)  solution  of  sodium  chloride  in  water;  a  3  per  cent  so- 
lution of  NaCl  may  also  be  used.  This  is  done  by  drawing 
up  the  blood  into  the  pipette  to  the  mark  ^  or  1,  and  then 
the  salt  solution  is  drawn  up  to  the  mark  100;  by  thor- 
oughly shaking  the  pipette  the  blood  is  mixed  well  with 
the  salt  solution.  After  blowing  out  the  liquid  contained 
in  the  capillary  portion  of  the  tube,  a  drop  of  the  mixture 
in  the  bulbous  portion  is  carefully  dropped  into  the  count- 
ing chamber,  a  cover-glass  is  applied,  and,  with  the  use  of 
the  microscope,  the  average  number  of  red  blood-corpuscles 
contained  in  one  square  of  the  counting  chamber — namely, 
in  4  yVu  cubic  millimetre — is  obtained  ;  this  again  is  multi- 
pHed  by  4,000,  and  the  resulting  number  is  again  multiphed 
by  200  if  the  dilution  of  blood  is  i  :  100,  and  by  100  if  the 
dilution  is  1  :  100;  the  result  is  the  number  of  red  blood- 
corpuscles  contained  in  one  cubic  millimetre  of  undiluted 
blood. 

The  origin  of    the    erythrocytes  in  embryonic    life  is 


40       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY'. 

believed  to  be  from  large  protoplasmic  spheres  in  which,  by 
an  endogenetic  process,  red  blood-corpuscles  are  formed; 
this  has  been  observed  to  take  place  in  the  chicken  in  the 
first  days  of  embryonic  life.  Later  on  such  protoplasmic 
spheres  in  which  red  corpuscles  have  formed  are  seen  in 
the  liver  and  spleen,  and  in  the  lymphatic  glands  surround- 
ing these.  The  corpuscles  formed  within  these  cells  con- 
tain HO  and  are  nucleated;  later  on  the  nucleus  disappears, 
the  protoplasmic  surrounding  shrinks,  and  finally  a  typical 
erythrocyte  appears.  In  post- embryonic  life  the  erythro- 
cytes are  found  within  the  large  so-called  vaso -formative 
cells  from  which  the  capillaries  are  formed.  In  later  hfe 
the  red  corpuscles  are  formed  in  the  red  marrow  of  the 
bones;  in  this,  nucleated  spherical  cells  appear  which  con- 
tain HO.  They  are  believed  to  be  leucocytes  in  a  transi- 
tional stage  in  the  formation  of  red  blood-corpuscles,  and 
they  are  therefore  called  erythrobkisfs. 

The  duration  of  the  life  of  the  red  blood-corpuscles  in 
our  body  is  short.  After  a  period  of  four  to  five  weeks 
they  undergo  a  process  of  destruction  believed  to  take 
place  in  the  liver,  because  the  blood  in  the  hepatic  vein 
shows  a  marked  decrease  in  the  number  of  red  corpuscles 
as  compared  with  the  blood  in  the  portal  vein. 

The  coloring  matter  and  other  ingredients  of  the  bile 
are  formed  as  the  result  of  the  destructive  process  of  the 
red  blood-corpuscles  in  the  liver. 

The  physiological  function  of  the  erythrocytes  is  the 
taking  of  oxygen  from  the  inspired  air  and  the  carrying 
of  it  to  the  tissues,  where  it  is  given  off  to  serve  as  an  oxi- 
dizing agent. 


LECTUEE  VII. 

THE   PHYSIOLOGY   OF   THE   BLOOD   {continued). 

B.  The  tvkite  or  colorless  corpuscles  were  first  observed  in 
the  human  blood  by  Hewson  in  1776.  They  are  spherical, 
having  a  granular  protoplasm,  generally  several  nuclei, 
but  no  cell-wall.  The  granules  of  the  protoplasm  are 
more  distinct  in  some  than  in  others,  and  also  differ  (ac- 
cording to  Ehrlich)  in  their  affinity  for  staining  agents 
which  vary  in  their  reaction;  thus  he  found  that  the  pro- 
toplasm granules  of  certain  corpuscles  have  a  peculiar 
affinity  for  acid,  others  for  basic,  and  again  others  for 
neutral  staining  agents,  and  he  called  the  granules  respec- 
tively eosinophile,  hasophile,  and  neutrophile  granules. 
Observations  are  of  no  little  importance  to  the  clinician, 
as  in  certain  pathological  conditions  the  one  or  the  other 
kind  of  these  granules  is  increased  or  prevalent.  For  in- 
stance, in  leukaemia  the  blood  contains  an  increased  num- 
ber of  white  corpuscles,  in  which  are  found  eosinophile 
granules;  in  inflammatory  conditions  colorless  blood-cor- 
puscles having  neutrophile  granules,  and  in  chronic  inflam- 
matory conditions  colorless  corpuscles  having  hasophile 
granules,  are  found  in  the  tissues  where  they  have  migrated 
from  the  blood.  The  nuclei  of  the  colorless  corpuscles  are 
not  clearly  visible,  but  become  so  upon  the  addition  of 
acetic  acid. 

The  size  of  the  colorless  corpuscles  varies.  In  human 
blood  three  sizes  are  found,  varying  in  diameter  from  -^-i^ 
to  tV  of  a  millimetre  ;  the  smallest  are  smaller  than  the 
erythrocytes  and  have  a  fine  granular  protoplasm  and 
generally  one  nucleus  ;  others  are  of  the  same  size  as  the 


42       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

erythrocytes,  and  again  others  are  considerably  larger ; 
these  generally  contain  very  refractive  protoplasmic  nuclei. 

The  specific  gravity  of  colorless  blood-corpuscles  is  but 
slightly  higher  than  that  of  the  plasma  (1027). 

The  chemical  composition  of  colorless  blood-corpuscles  is 
as  follows  :  albumin,  alkaline-albumin,  nucleo- albumin, 
nuclein,  glycogen,  cholesterin,  lecithin,  fat,  and  the  salts 
of  sodium,  potassium,  and  phosphorus. 

The  number  of  colorless  corpuscles  in  the  human  blood  is 
about  1  to  3  to  500  red  corpuscles.  This  proportion  varies 
greatly  in  different  locations  ;  venous  blood  generally  has 
more  colorless  corpuscles  than  arterial  blood. 

In  the  splenic  vein  the  proportion  is  1  white  to  60  red 
corpuscles  ;  in  the  splenic  artery  it  is  1  to  2,260  ;  in  the 
portal  vein  it  is  1  to  740,  and  in  the  hepatic  vein  1  to  170. 

The  number  of  colorless  corpuscles  is  generally  greater 
in  women  than  in  men,  and  greater  in  children  than  in 
grown  persons.  The  number  is  increased  during  the  pro- 
cess of  digestion,  during  menstruation,  after  a  loss  of  blood, 
after  childbirth,  when  tonic  drugs,  such  as  chinin,  nu- 
clein, etc. ,  are  taken.  The  number  is  very  much  increased 
in  a  pathological  condition  called  leuk2emia,  in  which  the 
proportion  is  sometimes  found  to  be  1  white  to  2  red  blood- 
corpuscles. 

The  number  is  decreased  during  fasting  and  when  the 
body  is  in  a  poorly  nourished  condition. 

The  counting  of  colorless  corpuscles  is  done  liy  a  method 
similar  to  that  employed  for  the  counting  of  erythrocytes, 
only  that  a  one-third  per  cent  solution  of  acetic  acid  is  used 
to  dilute  the  blood. 

The  origin  of  the  white  or  colorless  corpuscles  is  evi- 
dently in  the  spleen,  as  is  shown  by  the  enormous  quantity 
of  them  in  the  splenic  vein  as  compared  with  their  number 
in  the  blood  of  the  splenic  artery.  To  a  large  extent  the 
white  blood-corpuscles  originate  in  the  lymphatic  glands 
and  the  marrow  of  the  bones. 


THE   PHYSIOLOGY   OF   THE   BLOOD.  43 

White  blood-corpuscles  multiply  partly  by  mitosis,  partly 
by  amitosis. 

Cells  similar  or  identical  with  white  blood-corpuscles  are 
also  found  in  the  lymph,  chyle,  in  the  lymphoid  tissue,  in 
the  marrow  of  bones,  and  in  pus  ;  all  these,  including 
the  white  blood-corpuscles,  are  known  under  the  name  of 
leucocytes. 

Leucocytes  have  certain  characteristic  physiological  prop- 
erties, which  Max  Schiiltze,  Davaine.  Mefschnikoff,  and 
others  observed  and  described  ;  these  properties  are  amoe- 
l3oid  movement,  phagocytosis,  and  chemotaxis. 

The  amoeboid  movement  is  a  mode  of  locomotion  peculiar 
to  the  amoeba.  White  blood-corpuscles  normally  do  not 
■exhibit  this  property  in  the  circulating  blood,  but  they  can 
be  seen  to  pass  along  as  spherical  cells  in  the  current  of 
blood.  It  has  been  observed,  however,  that  in  inflamma- 
tory conditions  the  white  blood-corpuscles  migrate,  by 
means  of  this  peculiar  movement,  through  the  walls  of  the 
capillaries  and  through  the  tissues  to  the  area  of  inflam- 
mation. 

Phagocytosis  is  a  property  possessed  by  leucocytes  by 
which  they  can  take  up  and  absorb  substances  such  as 
pigment,  micro-organisms,  bacteria,  many  pathogenic  prod- 
ucts, and  products  of  retrogressive  processes  in  the  tissues. 
Mefschnikoff,  who  studied  this  function,  termed  it  phagocy- 
tosis, and  the  cells  possessing  it,  phagocytes.  It  is  believed 
that  in  the  resorj)tion  of  the  deciduous  teeth  phagocytes 
take  up  the  granules  of  the  inorganic  matter. 

Chemotaxis,  or  chemotropimiis,  is  another  characteristic 
property  possessed  by  the  leucocytes.  It  consists  in  their 
peculiar  tendency  to  migrate  toward  the  seat  of  certain 
substances,  particularly  toward  the  seat  of  products  of 
degenerative  processes  and  pathogenic  micro-organisms. 
For  instance,  if  staphylococci  are  introduced  at  some  part 
of  the  body,  the  leucocytes  migrate  toward  them  by  virtue 
of    their    property  of  amoeboid  movement,  and,  having 


44      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

reached  their  seat,  the  phagocytes  will  take  up  into  them- 
selves the  bacteria  and  tend  to  destroy  them. 

It  is  beheved  that  white  blood-corpuscles  also  take  part 
in  the  coagulation  of  the  blood.  When  blood  is  taken 
from  the  circulation  it  will  be  found  that  a  great  portion 
of  its  white  corpuscles  are  destroyed  ;  and  it  is  believed 
that  certain  substances  in  these  have  a  fibrin-forming 
quality.  In  certain  infectious  diseases,  such  as  septica?mia, 
so-called  thrombi  are  found  within  the  veins.  These  are 
formed  from  coagulated  blood,  and  are  believed  to  be  the 
result  of  a  destruction  of  white  corpuscles  and  subsequent 
coagulation  of  blood  within  the  vessels. 

C.  The  Blood-Pkdes. 

The  blood-plates  or  plaques  are  small,  pale  discs  averaging 
in  size  from  -^^  to  3^^  of  a  millimetre  in  diameter.  They 
have  no  characteristic  structure.  Their  number  is  about 
200,000  to  250,000  in  one  cubic  millimetre  of  blood.  It  is 
believed  that  they  are  an  important  factor  in  the  fibrin 
formation  in  coagulating  blood. 

D.  Tlie  Elementary  Granules. 

In  the  blood  there  are  also  a  number  of  minute,  irregular 
granules  which  are  thought  to  be  protoplasmic  masses  re- 
sulting from  the  breaking-up  of  red  and  white  corpuscles 
in  the  blood. 

II.    THE   PLASMA. 

The  blood-plasma,  or  liquor  sanguinis,  is  the  fluid  me- 
dium in  which  the  histological  elements  already  descril)ed 
float.  Plasma  is  a  thickish,  sticky  fluid.  Its  reaction  i& 
neutral,  its  color  yellowish,  and  its  specific  gravity  1027. 

The  composition  of  plasma  is  as  follows  : 

1.  Water,  90  per  cent. 

2.  Inorganic  salts,    0.85   per  cent.     These  are    sodium 


THE   PHYSIOLOGY   OF   THE   BLOOD.  45 

chloride,  sodium  sulphate,  sodium  carbonate,  sodium  phos- 
phate, calcium  phosphate,  and  magnesium  phosphate. 

3.  Fats,  0.1  to  0.2  per  cent— namely,  olein,  palmetin, 
stearin,  cholesterin. 

4.  Grape  sugar,  traces  of  which  are  contained  in  the 
blood  of  the  hepatic  vein. 

5.  Excrementitious  substances,  such  as  urea,  kreatin, 
uric  acid,  etc.  These  are  more  abundant  after  the  taking 
of  nitrogenous  foods. 

6.  Albuminoid  substances,  8  to  10  per  cent  ;  among 
these  are  serum-albumin,  serum-globulin,  fibrinogen.  Of 
these  about  0.2  per  cent  are  fibrin-forming  substances. 

7.  A  yellowish  coloring-substance. 

8.  G-ases— namely,  oxygen,  nitrogen,  and  carbon  dioxide. 

The  Gases  of  the  Blood. 

It  is  an  established  fact  that  between  the  particles  of  a 
porous  substance  and  between  the  particles  of  gases  there 
exists  an  affinity  which  manifests  itself  in  the  absorption 
of  gases  by  porous  solids.  This  same  affinity  exists  between 
the  particles  of  liquids  and  of  gases.  It  is,  for  instance, 
well  known  that  water  absorbs  oxygen  from  the  air.  The 
volume  of  gas  which  substances  absorb  is  equal  under 
various  conditions  of  pressure,  but  an  increased  pressure 
increases  the  quantity  or  weight  of  the  gas  in  that  volume. 
It  follows,  therefore,  that  the  quantity  of  gas  absorbed  by 
a  substance  can  be  diminished  by  diminishing  the  outside 
pressure  of  that  gas.  This  is  accomplished  by  means  of  an 
air-pump.  Absorbed  gases  can  also  be  removed  by  heat, 
which  decreases  the  absorbing  power  of  the  substance  hold- 
ing the  gases. 

The  phenomenon  of  the  diffusion  of  gases  is  also  used  to 
determine  the  character  of  the  absorbed  gas  or  gases. 

The  law  of  the  diffusion  of  gases  is,  that  when  gases  are 
brought  together  which  do  not  chemically  combine,  their 
molecules  will  diffuse,    independent   of    their    respective 


4G      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

weights,  until  an  equal  mixture  of  the  gases  has  taken 
place.  This  diffusion  of  gases  also  takes  place  through  por- 
ous solids,  and  between  the  molecules  of  gases  absorbed  in 
liquids  and  those  not  absorbed. 

It  follows,  therefore,  that  gases  absorbed  by  a  liquid  can 
be  removed  from  it  by  bringing  the  substance  in  contact 
with  another  gas,  when,  according  to  the  law  of  the  dif- 
fusion of  gases,  the  particles  of  gas  absorbed  in  the  sub- 
stance will  mix  with  the  particles  of  the  gas  surrounding 
the  substance  until  an  equal  mixture  of  the  two  gases  has 
taken  place. 

The  gases  contained  in  the  human  blood  are  oxygen, 
nitrogen,  and  carbon  dioxide;  they  are  partially  absorbed 
by,  and  partially  chemically  combined  with,  substances  of 
the  blood. 

The  oxygen  contained  in  arterial  blood  is  about  17  pel* 
cent  by  volume;  the  quantity  in  venous  blood  is  much  less. 
Only  a  small  quantity  of  oxygen  is  absorbed  by  the  plasma 
of  the  blood.  This  quantity  is  equal  to  the  amount  of 
oxygen  which  distilled  water  would  absorb  at  a  pressure 
equal  to  that  of  the  oxygen  in  the  air  of  the  lungs  heated 
to  a  temperature  equal  to  that  of  the  blood . 

The  greater  portion  of  the  oxygen  of  the  blood  is  com- 
bined chemically  with  the  haemoglobin  of  the  erythrocytes. 
One  gramme  of  HO  w411  combine  with  1.5  cubic  centi- 
metres of  oxygen  at  ordinary  atmospheric  pressure. 

The  oxygen  can  all  be  removed  from  the-  blood  by  the 
use  of  the  air-pump,  by  heat,  and  by  treating  with  other 
gases.  Chemical  processes  may  also  be  employed,  but  are 
not  necessary,  because  the  combination  of  the  oxygen  with 
H(J  is  but  a  very  loose  one. 

The  quality  and  quantity  of  the  gas  eliminated  from  the 
blood  are  determined  by  applying  the  common  chemical 
tests  for  oxygen. 

Human  blood  contains  about  li  per  cent  of  nitrogen  (by 
volume);  this  is  mostly  absorbed  by  the  plasma,   but  a 


THE   PHYSIOLOGY   OF   THE   BLOOD.  47 

small  portion  is  held  in  chemical  combination  in  the  cor- 
puscles, etc. 

Carhon  dioxide  (CO^)  is  also  contained  in  the  blood,  par- 
tially in  simple  solution,  to  a  greater  extent  in  chemical 
combination  with  the  substances  contained  in  the  plasma, 
particularly  with  the  carbonates,  and  also  with  the  red  and 
white  blood-corpuscles.  Arterial  blood  contains  about  30 
per  cent  (by  volume),  venous  blood  a  larger  percentage,  of 
carbon  dioxide. 

Tlie  total  quantity  of  blood  in  the  human  body  is  about 
•5^  to  -jV  of  the  body  weight. 

Arterial  blood  differs  from  venous  blood  in  the  following 
points : 

1.  It  is  bright  red. 

2.  It  is  generally  one  degree  warmer. 

3.  It  contains  more  0  and  less  C0„. 

4.  It  contains  more  water,  more  fatty  matter,  more  su- 
gar, and  more  salts. 

5.  It  contains  a  smaller  quantity  of  red  corpuscles. 

6.  It  contains  less  excrementitious  substances,  such  as 
urea,  etc. 

The  uses  of  the  blood  may  be  enumerated  as  follows : 

1.  To  act  as  a  medium  for  the  reception  of  the  materials 
intended  for  'the  nutrition  of  the  body. 

2.  To  act  as  a  medium  by  which  the  nutritive  materials 
are  conveyed  to,  and  the  Avaste  materials  from,  the  tissues. 

3.  To  act  as  a  medium  for  the  exchange  of  gases  in  the 
lungs  and  in  the  tissues. 

4.  To  distribute  warmth  to  all  parts  of  the  body. 

5.  To  give  pliability  to  the  texture  of  many  tissues. 

6.  To  furnish  the  secreting  glands  with  the  materials 
required  for  their  secretion. 

In  order  that  the  blood  may  properly  serve  its  uses  it 
must  contain  its  many  ingredients  in  proper  quantity  and 
quality,  and,  since  many  pathological  conditions  depend 
upon  this,  it  is  essential  that  the  clinician  be  able  to  test 


48      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

and  examine  the  quantity  and  quality  of  the  blood  ingre- 
dients. The  more  common  methods  of  examination  of  the 
principal  blood  ingredients  I  have  .already  mentioned  and 
described;  the  more  complicated  tests  will  be  brought  to 
your  notice  in  your  practical  course  in  physiological  chem- 
istry. 

I  will  only  mention  at  this  time  some  of  the  pathological 
conditions  which  depend  upon  changes  in  the  quality  or 
quantity  of  blood  constituents. 

Plethora,  or  polysemia,  is  an  increase  of  the  total  amount 
and  of  the  constituents  of  the  blood.  It  is  caused  mainly 
by  an  excessive  nutritive  process.  This  condition  is  recog- 
nized by  an  increased  blood-pressure,  full  veins,  red  color, 
congestion,  and  a  hard,  strong  pulse.  The  condition  be- 
comes dangerous  when  the  blood-pressure  is  so  increased 
that  a  rupture  of  the  wall  of  a  blood-vessel  may  occur. 

Polycemia  serosa  is  a  condition  in  which  the  watery  part 
of  the  blood  is  increased;  it  occurs  often  in  diseases  in 
which  the  secretory  function  of  the  kidneys  is  interfered 
with. 

Leukcemia  is  the  excessive  increase  of  white  blood-cor- 
puscles, and,  according  to  the  seat  of  the  increase  of  the 
leucocytes,  we  classify  it  as  myelogenetic,  splenic,  and 
lymphatic  leukaemia. 

Ancemia  is  a  condition  characterized  by  a  diminution  of 
HO. 

Progressive  pernicious  anoimia  is  a  condition  character- 
ized by  the  impairment  of  the  functions  of  the  organs  in 
which  the  blood  constituents,  principally  the  erythrocytes, 
originate. 

Chlorosis  is  a  condition  in  which  we  find  a  lack  of  devel- 
opment and  weakness  in  the  circulatory  apparatus  and  a 
disturbance  of  the  blood-forming  organs. 

Besides  these  pathological  conditions  mentioned,  there 
are  many  others  dependent  upon  a  change  in  form,  size, 
and  function  of  the  blood-corpuscles,  or  upon  an  increase 


THE   PHYSIOLOGY   OF   THE    BLOOD.  49 

or  decrease  of  the  constituents  of  the  plasma.  We  find,  for 
instance,  conditions  in  which  the  albuminous  matter  of  the 
plasma  is  increased  or  decreased,  those  in  which  the  fatty 
matter  is  increased,  and  those  in  which  the  carbohydrate 
matter  is  increased.  In  many  febrile  diseases  an  increase 
of  fibrin-forming  substances  has  been  observed.  Of  late 
considerable  importance  has  been  attached  to  the  fact  that, 
in  many  diseases  deiDending  upon  bacteria,  the  character- 
istic bacteria  of  those  diseases  have  been  detected  in  the 
blood.  I  will  mention  here  only  the  micro-organism  of 
malarial  fever  (plasmodium)  and  that  of  typhoid  fever. 

From  the  foregoing  it  will  be  clear  to  you  that  the  exami- 
nation of  the  blood  is  an  important  point  in  the  diagnosis 
of  many  diseases,  and  that  in  order  to  understand  or  detect 
any  changes  in  the  blood  it  is  essential  to  fully  understand 
the  composition,  physical  and  chemical  properties,  and  the 
histology  and  physiology  of  normal  blood. 

4 


LECTUKli:  A^JII. 

THE   COAGULATION   OF   THE   BLOOD. 

In  my  last  lecture  I  finished  the  description  of  the  nor- 
mal human  blood,  and,  for  a  better  understanding  of  the 
subject  of  this  lecture,  I  will  repeat  that  normal  circulat- 
ing blood  consists  of  the  plasma,  or  liquor  sanguinis,  and 
of  the  blood-corpuscles  suspended  in  it.  The  coagulation 
of  the  blood  is  a  phenomenon  consisting  in  the  separation 
of  the  blood-constituents  into  a  clot  and  the  serum. 

The  clot  is  a  soft,  jelly-like  mass,  reddish-white  in  color, 
composed  of  the  blood-corpuscles  held  together  by  a  net- 
work of  delicate  fibrillae. 

The  serum  is  the  i)lasma  minus  the  fibrinogen  ;  its  spe- 
cific gravity  is  1028,  and  its  alkalinity  is  about  one-half 
that  of  the  blood;  it  is  a  clear,  almost  colorless  fluid. 

Process  of  Blood  Coagulation. 

Circulating  blood  normally  does  not  coagulate  when  the 
inner  surface  of  the  blood-vessels  is  in  a  normal  condition. 

When  blood  is  taken  from  the  circulation  into  some  ves- 
sel, it  will  very  soon  be  noticed  that  the  blood  separates  into 
two  parts — first,  a  soft,  gelatin-like  mass  which  sinks  to  the 
bottom  and  assumes  the  shape  of  the  vessel;  and  second,  a 
clear  fluid,  the  serum,  covering  the  gelatin-like  mass.  In 
from  two  to  fifteen  minutes  it  can  be  seen  that  fine  fibrillse 
begin  to  form  upon  the  surface  of  the  gelatin-like  mass. 
In  about  twelve  to  fifteen  hours  it  will  be  found  that  the 
whole  mass  is  permeated  by  these  delicate  fibrillte,  so  that 
it  can  be  cut ;  this  is  the  clot.     In  conditions  where  the 


THE   COAGULATION   OF   THE   BLOOD.  51 

process  of  coagulation  is  retarded,  as  it  is  in  the  case  of 
febrile  conditions,  in  chlorosis,  and  in  hydrsemia,  the  clot 
has  a  whitish  surface,  due  to  the  fact  that  the  erythrocytes 
sink  to  the  bottom  before  the  coagulation  takes  place.  This 
is  the  case  whenever  in  the  blood  the  specific  gravity  of 
the  erythrocytes  is  increased,  or  when  that  of  the  plasma 
is  decreased.  These  conditions  are  present  in  the  diseases 
mentioned  above. 

The  blood- coagulation  is  therefore  due  to  fibrin  forma- 
tion. 

When  freshly-drawn  blood  is  beaten  with  a  stick,  fibrin 
can  be  obtained  in  the  form  of  delicate  fibrillfe,  which  col- 
lect around  the  stick;  blood  so  treated  is  termed  defihrinatecl 
blood. 

Fibrin  consists  of  delicate  elastic  fibriUse.  It  is  insoluble 
in  water  and  ether,  and  when  treated  Avith  hydrochloric 
acid  is  transformed  into  xantonin. 

According  to  Alexander  Schmidt,  fibrin  is  formed  by  the 
union  of  two  constituents  of  the  plasma  in  the  presence  of 
a  ferment.  These  two  substances  are  fibrinogen  and 
fibrinoplastin ;  they  are  both  albuminous,  belonging  to 
the  class  of  globuhns.  They  are  contained  in  solution  in 
the  plasma  and  do  not  differ  much  in  their  chemical  com- 
position. 

Fibrinoplastin,  also  called  serum-globulin  or  para- 
globulin,  can  be  precif)itated  by  the  addition  of  magnesium 
sulphate  ;  it  is  soluble  in  a  10  per  cent  solution  of  sodium 
chloride.  Fibrinoplastin  is  best  obtained  from  serum  by 
precipitating  it  in  the  manner  indicated. 

Fibrinogen  is  the  substance  which  forms  the  main  mass 
of  the  fibrin  ;  it  is  best  obtained  from  hydrocele  fluid  and 
from  the  serous  secretions  of  the  pericardium,  the  pleura, 
etc.,  from  which  it  is  precipitated  by  the  saturation  of 
these  fluids  with  sodium  chloride.  The  two  fibrin-forming 
substances  are  soluble  in  dilute  solutions  of  alkalies,  of 
sodium  chloride,  and  of  hydrochloric  acid. 


52      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Fibrinogen  differs  from  fibriuoplastin  in  that  the  former 
may  be  more  readily  precipitated  and  dissolved  again. 

The  fibrin-ferment  is  obtained  by  treating  blood -serum 
with  strong  alcohol;  the  resulting  precipitate,  composed  of 
albumin  and  the  ferment,  is  dried,  pulverized,  and  then 
treated  with  water  and  filtered;  the  fibrin-ferment,  being 
soluble  in  water,  passes  through  the  filter  and  so  is  sepa- 
rated from  the  albumin.  If  solutions  of  the  three  fibrin- 
forming  substances  are  mixed  the  formation  of  fibrin  will 
at  once  take  place  ;  the  presence  of  oxygen  and  sodium 
chloride  is  essential  for  the  process  ;  a  temperature  of 
about  9S.6°  is  preferable. 

The  fibrin-forming  substances  constitute  about  0.2  per 
cent  of  all  the  albuminous  substances  of  the  plasma.  Ac- 
cording to  Alexander  Schmidt,  the  fibrin-forming  sub- 
stances originate  mainly  in  the  leucocytes,  although  fibrin- 
ogen,  and  probably  fibrin-ferment,  are  already  contained 
in  solution  in  the  plasma  of  the  circulating  blood. 

When  blood  is  drawn  from  the  circulation  numerous 
leucocytes  are  destroyed.  The  products  of  this  breaking- 
up  dissolve  in  the  plasma,  and  some  of  them  form  the 
fibrinoplastic  substance. 

I  have  already  stated  in  a  previous  lecture  that  in  cer- 
tain pathological  conditions,  such  as  septicaemia,  in  which 
a  breaking-down  of  the  leucocytes  takes  place  in  the  circu- 
lating blood,  portions  of  coagulated  blood  are  formed  in  the 
veins,  called  thrombi. 

Further  observations  have  revealed  the  fact  that  the 
erythrocytes  also  have  a  part  in  the  formation  of  the 
fibrin. 

Landois  has  been  able  to  observe  the  formation  of  fibrin 
from  the  stroma  of  erythrocytes  of  mammalia.  The  fibrin 
may  therefore,  in  accordance  with  its  origin,  be  divided 
into  plasma-fibrin  and  stroma-fibrin.  It  has  been  observed 
that  substances  which  dissolve  erythrocytes  produce  a 
rapid  coagulation  of  the  blood. 


THE    COAGULATION   OF   THE   BLOOD.  53 

The  coagulation  of  the  blood  is  retarded  or  entirely  pre- 
vented by:  ' 

1.  The  addition  of  alkalies,  such  as  ammonia. 

2.  The  addition  of  saturated  solutions  of  certain  salts, 
such  as  carbonates,  phosphates,  sulphates,  especially  mag- 
nesium sulphate. 

3.  Cold,  freezing. 

4.  High  pressure. 

5.  Addition  of  acetic  acid  until  an  acid  reaction  is  ob- 
tained. 

6.  Increased  amount  of  COo. 

7.  The  addition  of  egg-  albumen,  of  a  solution  of  sugar, 
of  glycerin,  of  great  quantities  of  water. 

8.  The  addition  of  pancreatic  and  diastatic  ferments. 
Menstrual  blood  and  that    of   haemophiles    show  very 

little  tendency  to  coagulate. 

Conditions  hastening  the  coagulation  of  blood  are: 

1.  Contact  with  foreign  substances  to  which  the  blood 
can  adhere;  for  instance,  threads,  needles,  wire,  etc.,  in- 
troduced into  the  blood-vessels. 

2.  Heat. 

3.  Air. 

4.  Products  of  the  retrogressive  changes  of  albuminous 
substances,  such  as  uric  acid,  leucin,  taurin,  lecithin,  etc. 

5.  Certain  chemicals,  mainly  acids  in  small  quantities. 
Blood  does  not   normally  coagulate  when  circulating, 

provided  the  endothelial  lining  of  the  vessels  is  intact;  if 
this  is  roughened  by  inflammation  or  by  traumatism,  a 
clot  will  be  deposited  upon  the  roughened  surface. 

When  blood  is  stagnant  in  the  vessels  coagulation  does 
not  take  place  rapidly,  but  a  clot  will  gradually  form  in  the 
centre  of  the  vessel  where  the  blood  does  not  come  in  con- 
tact with  the  epithelial  lining. 

Before  finishing  the  subject  of  the  physiology  of  the 
blood,  I  will  consider  a  subject  to  which  of  late  years 
much  attention  has  been  paid.     I  refer  to  the  serum  treat- 


54     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

ment,  which  to-day  is  employed  in  many  diseases — viz.^ 
in  infections,  or  such  diseases  as  depend  upon  the  develop- 
ment of  specific  jjoisons  and  micro-organisms  such  as 
bacteria. 

Blood  and  the  serum  of  blood  possess  a  germicidal  prop- 
erty; that  means  a  property  to  destroy  bacteria.  This 
property  of  the  blood  is  believed  to  be  due  to  certain  albu- 
minous and  mineral  ingredients,  the  removal  of  which 
destroys  this  power  of  the  blood  and  serum;  heat  and  ex- 
posure to  light  have  the  same  effect. 

It  has  been  demonstrated  by  experiments  that  individ- 
uals are  immunized  against  certain  infectious  diseases  by 
repeated  inoculations  with  the  poison  or  micro-organisms 
of  such  diseases;  furthermore,  it  has  been  demonstrated 
that  the  blood  or  serum  of  individuals  so  inoculated  de- 
stroys the  poison  or  micro-organisms  of  the  disease. 
These  facts  are  utilized  to-day  very  extensively  not  only 
in  the  curative  but  also  in  the  prophylactic  treatment  of 
many  infectious  diseases,  such  as  tuberculosis,  diphtheria,, 
hydroi^hobia,  tetanus,  etc.  For  a  better  understanding  I 
will  describe  to  you  the  mode  of  preparation  and  the  use 
of  the  diphtheria  antitoxin,  which  now  is  most  exclusively 
used  by  every  scientific  practitioner  of  medicine  in  the 
treatment  of  that  dreadful  disease,  diphtheria,  against 
which,  for  so  many  years,  medical  science  and  skill  was 
apparently  powerless.  The  great  success  of  this  treatment 
is  shown  by  the  marked  decrease  in  the  percentage  of 
deaths  from  the  disease.  To-day  the  health  department 
of  almost  every  large  city  prepares  diphtheria  antitoxin^ 
so  that  even  the  poorest  may  reap  the  benefit  of  this  pre- 
paration, formerly  so  expensive. 

The  constant  observations  of  the  experienced  medical 
inspectors  of  the  Health  Department  show  that  the  dis- 
ease can  be  thus  successfully  combated  in  most  cases,  if 
used  properly  and  at  the  right  stage  of  the  disease.  In- 
deed, the  preparation  is  frequently  used  as  a  preventive 


QUESTIONS  AND  EXERCISES.  55 

of  the  disease,  in  the  same  way  as  vaccine  virus  is  used  to 
prevent  small-pox.  To-day  members  of  a  household  in 
which  diphtheria  has  appeared  are  inoculated  with  the  an- 
titoxin to  prevent  infection,  and  observations  and  statistics 
show  that  this  is  actually  accomplished  by  such  treatment. 

The  discovery  of  the  diphtheria  antitoxin  is  the  result  of 
the  studies  of  Beliring,  of  Berlin,  and  of  Pasteur,  of  Paris. 

To  Dr.  H.  M.  Biggs,  chief  pathologist  of  the  Health  De- 
partment of  this  city,  the  credit  is  due  of  having  created  a 
special  department  for  the  diagnosis  and  treatment  of  diph- 
theria, and  special  laboratories  for  the  preparation  of  the 
diphtheria  antitoxin,  so  that,  as  stated  before,  the  anti- 
toxin may  be  obtained  even  by  the  poorest. 

The  method  of  the  preparation  of  the  diphtheria  anti- 
toxin employed  by  the  Health  Department  of  this  city  is 
as  follows:  Perfectly  healthy  horses,  kept  especially  for 
that  purpose,  are  repeatedly  inoculated  until  a  condition  is 
obtained  where  inoculation  fails  to  cause  the  characteristic 
symptoms.  Blood  is  then  drawn  from  the  immunized  ani- 
mal. The  serum  of  this  blood  is  aseptically  prepared  in 
certain  strengths,  and  is  the  antitoxin  as  it  is  used.  The 
strength  of  the  solution  is  given  in  antitoxin  units. 


QUESTIONS   AND   EXERCISES. 

Subject. — Tlie  Physiology  of  the  Blood. 
Lectures  VI.-VIIL  inclusive. 

69.  What  is  the  blood  ? 

70.  Why  is  human  blood  opaque  ? 

71.  What  is  the  color  of  human  blood  j 

72.  What  is  the  coloring  matter  of  the  blood  I 

73.  Why  is  blood  light  in  the  arteries  and  dark  in  the 
veins  ? 

74.  What  is  the  specific  gravity  of  the  blood  ? 


56       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

75.  State  conditions  in  which  the  specific  gravity  of  the 
blood  is  increased  and  those  in  which  it  is  decreased. 

76.  What  is  the  reaction  of  human  blood  ? 

77.  Name  some  of  the  conditions  which  lessen  and  some 
which  increase  the  alkalinity  of  the  blood. 

78.  How  would  you  ascertain  the  relative  alkalinity  of 
the  blood  ( 

7'J.  What  is  the  odor  of  human  blood  ? 

80.  What  is  the  taste  of  human  blood  i 

81.  Name  the  morphological  elements  of  the  blood. 

82.  Why  is  blood  considered  a  tissue  ? 

83.  By  whom  were  the  red  blood-corpuscles  first  observed 
in  human  blood  ?    When  ? 

Si.  Describe  the  structure  of  a  red  blood-corpuscle. 

85.  Name  the  physical  properties  of  red  blood-corpuscles. 

86.  What  is  the  chemical  composition  of  red  blood-cor- 
puscles ? 

87.  Give  the  measures  of  a  red  blood-corpuscle. 

88.  State  the  physiological  functions  of  the  red  blood- 
corpuscles. 

89.  What  is  hsemoglobin  (    Describe  it. 

90.  Give  the  composition  of  HO. 

91.  What  is  haematin  i  Haematoidin  (  MetHO,  0-HO, 
and  CO-HO?  State  where  and  under  what  condition  they 
are  found  in  the  human  body. 

92.  What  is  the  usual  difference  in  shape  between  the 
red  corpuscles  of  the  blood  in  the  mammalia  and  those  of 
the  ovipara  ? 

93.  Mention  some  of  the  mammalia  which  do  not  have 
circular,  disc-like  red  blood-corpuscles. 

94.  Describe  the  process  by  which  you  can  obtain  haema- 
tin crystals  from  old  blood-stains. 

95.  What  is  the  number  of  red  blood-corpuscles  in  1 
cubic  millimetre  of  human  blood  ? 

96.  Describe  the  process  of  counting  the  red  blood-cor- 
puscles. 


QUESTIONS   AND   EXERCISES.  57 

'97.  Name  the  origin  of  the  red  blood  corpuscles. 

98.  State  the  average  duration  of  life  of  a  red  blood- 
•corpuscle. 

99.  Where  are  the  red  blood-corpuscles  destroyed  in  the 
body  ?    Mention  facts  sustaining  your  statement. 

100.  Name  liquids  in  which  red  blood- corpuscles  can  be 
preserved. 

101.  What  is  the  quantity  of  HO  in  the  blood,  and  how 
can  this  be  determined  ( 

102.  How  much  iron,  by  weight,  does  HO  contain  i 

103.  What  is  00  ?    What  takes  place  when  it  is  inhaled, 
.and  what  are  the  symptoms  of  CO  poisoning  I 

104.  Give  the  treatment  for  CO  poisoning. 

105.  When  is  transfusion  of  blood  required  (    Mention 
objections  to  this  operation. 

106.  Describe  the  Abbe-Zeiss  counting  apparatus. 

107.  Describe  the  shape,  size,  and  structure  of  a  white 
blood-corpuscle. 

108.  What    is    meant  by    eosinophile,    basophile,     and 
neutrophile  protoplasm  granules  in  the  white  blood- cor- 


puscles ? 

109.  Give  the  chemical  composition  of  white  blood-cor- 
puscles. 

110.  AVhatis  the  number  of  white  blood-corpuscles  (a)  at 
different  ages,  (6)  in  different  sexes,  and  (c)  in  the  differ- 
ent locations. 

111.  Mention  bodily  states  in  which  the  number  of  white 
blood-corpuscles  is  increased,  and  those  in  which  it  is  de- 
•creased. 

112.  Name  the  process  of  counting  white  blood-cor- 
puscles. 

113.  Give  the  origin  of  the  white  blood-corpuscles  in 
the  body. 

114.  What  are  leucocytes  ? 

115.  What  are  the  physiological  properties  of  leucocytes  ? 

116.  What  is  chemotaxis  ? 


58       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

117.  What  is  phagocytosis  ? 

118.  What  are  the  blood-plaques  ?    Describe  them. 

119.  What  are  the  elementary  granules  seen  in  the 
blood  ? 

120.  What  is  liquor  sanguinis  ? 

121.  Give  the  composition  of  plasma. 

122.  What  is  the  reaction  and  specific  gravity  of  the 
plasma  ? 

123.  Name  the  gases  of  the  blood.  How  and  where  are 
they  contained  in  the  blood,  and  how  can  they  be  elimi- 
nated from  it  ? 

124.  What  is  the  total  quantity  of  blood  in  the  human 
body  ? 

125.  What  are  the  differences  between  arterial  and 
venous  blood  ? 

126.  What  are  the  uses  of  the  blood  ? 

127.  Name  some  bodily  states  in  which  ingredients  of 
the  blood  are  increased  or  decreased. 

128.  What  is  meant  by  the  coagulation  of  the  blood  ? 

129.  What  is  a  clot  ? 

130.  What  is  the  serum  ? 

131.  What  is  the  composition  of  serum  ? 

132.  Describe  the  process  of  blood-coagulation. 

133.  To  what  is  the  coagulation  of  the  blood  due  ? 

134.  Name  the  fibrin-forming  substances. 

135.  How  can  the  fibrin  forming  substances  be  obtained? 

136.  How  is  blood  defibrinated  ? 

137.  State  what  part  the  corpuscles  take  in  blood-coagu- 
lation, and  mention  facts  sustaining  your  statement. 

138.  What  favors  and  what  retards  blood-coagulation  ? 

139.  What  is  a  haemophile  ? 

140.  What  do  you  understand  by  the  serum  theory,  and 
upon  what  peculiar  property  of  the  blood  or  serum  is  it 
based  ? 

141.  Describe  the  preparation  and  use  of  the  diphtheria 
antitoxin. 


QUESTIONS  AND  EXERCISES.  59 

142.  What  do  you  understand  by  toxins  ? 

143.  What  are  bacteria  ? 

144.  What  do  you  understand  by  immunization  ? 

145.  Name  conditions  in  which  bacteria  are  found  in 
the  blood. 


LECTURE    IX. 

THE   CHEMICAL  INGREDIENTS   OF   THE   HUMAN   ORGANISM. 

It  has  been  found  that  about  seventeen  of  the  sixty- seven 
or  seventy  chemical  elements  exist  in  the  fluids  and  tissues 
of  the  human  organism.  These  seventeen  elements  are  : 
oxygen,  carbon,  hydrogen,  nitrogen,  calcium,  phosphorus, 
sodium,  potassium,  silicon,  magnesium,  chlorine,  fluorine, 
sulphur,  iron,  manganese,  copper,  and  aluminium. 

They  are  found  in  the  human  body  in  the  following  ap- 
proximate proportion  :  oxygen,  Y20in  1,000  parts;  carbon, 
135;  hydrogen,  90;  nitrogen,  25;  calcium,  10;  phosphorus, 
1;  sodium,  1  ;  and  the  remaining  ten  elements,  8  parts. 
These  elements  exist  in  the  human  body  in  the  form  of 
chemical  compounds,  with  the  exception  of  oxygen  and 
nitrogen,  which  exist  in  a  free  state. 

The  chemical  substances,  elementary  or  compound,  which 
normally  exist  in  the  body,  and  which  can  be  extracted 
from  it  in  the  form  in  which  they  exist,  are  known  as  the 
proximate  principles. 

The  proximate  principles  are  divided  into  (1)  Inorganic, 
(2)  Organic. 

I.     THE   INORGANIC   PROXIMATE    PRINCIPLES. 

The  substances  of  this  class  originate  in  the  inorganic 
world.  They  are  generally  taken  into  the  body  with  the 
food,  drink,  or  air,  but  sometimes  they  are  the  result  of 
chemical  processes  in  the  body;  they  are  eliminated  gene- 
rally in  their  own  form  with  the  secretions. 

The  substances  of  this  group  are:  1,  water;  2,  inorganic 
salts;  3,  inorganic  acids;  4,  gases;  5,  metals. 


CHEMICAL   INGREDIENTS    OF    THE   HUMAN   ORGANISM,         Gl 

1.  Water  constitutes  58.5  per  cent  of  the  whole  organism. 
and  is  found  in  all  fluids  and  tissues.  It  serves  to  ren- 
der the  tissues  soft  and  pliable,  and  also  acts  as  a  medium 
for  the  suspension  or  solution  of  the  fluid  ingredients  of 
the  body.  The  soft  tissue  of  the  kidneys  has  the  greatest 
percentage  of  water — namely,  82.5  per  cent;  bone  contains 
22  per  cent,  teeth  10  per  cent,  and  the  enamel  of  the  teeth 
0.2  per  cent. 

The  water  in  the  body  is  generally  taken  in  as  such  with 
the  food  and  drink,  but  a  small  amount  is  formed  within 
the  body.  Water  is  eliminated  from  the  body,  as  such, 
through  the  kidneys,  skin,  and  with  the  faeces. 

2.  The  inorganic  salts  contained  in  the  body  are  the 
chlorides  of  sodium  and  potassium,  the  carbonates  of 
sodium  and  potassium,  the  phosphates  of  sodium  and  potas- 
sium, the  sulphates  of  sodium  and  potassium,  the  phos- 
phates and  carbonates  of  magnesium,  and,  besides  these, 
small  quantities  of  fluoride  and  carbonate  of  calcium,  chlo- 
ride of  ammonium,  and  bicarbonate  of  soda. 

Sodium  chloride  is  probably  contained  in  the  body  in  a 
greater  quantity  than  any  other  salt ;  this  is  estimated  to 
be  110  grammes  in  the  adult.  It  is  taken  in  as  such  as  an 
essential  constituent  of  the  food,  and  is  excreted  in  its  own 
form  with  the  urine  and  the  sweat;  the  quantity  thus  dis- 
charged in  twenty-four  hours  is  estimated  to  be  15  grammes. 
This  salt  is  contained  in  almost  all  fluids,  tissues,  and  secre- 
tions of  the  body;  its  main  use  is  to  favor  certain  physical 
processes,  such  as  solubility,  absorption,  osmosis,  etc. 

Potassium  chloride  is  also  contained  in  many  tissues  and 
fluids  of  the  body,  but  the  total  quantity  is  less  than  that 
of  sodium  chloride.  In  muscle  and  in  milk  it  is  more 
abundant  than  the  former  salt.  Its  uses  in  the  organism 
are  the  same. 

The  sidphates  are  taken  in  as  such  with  the  food,  but  to 
some  extent  they  are  formed  within  the  body  as  a  product 
of  the  decomposition  of  albuminoid  substances.     They  are 


62       LECTURES  ON  HUMAN   PHYSIOLOGY  AND   HISTOLOGY. 

eliminated  chiefly  with  the  urine.  They  exist  only  in 
small  quantities,  principally  in  the  urine,  hair,  and 
nails. 

The  X)1iosphcites  are  more  abundant.  The  so-called  al- 
kaline phosphates  are  the  salts  which  maintain  the  reac- 
tion of  the  many  alkaline  fluids  in  the  body.  The  neutral 
phosphates  constitute  part  of  the  inorganic  basis  of  the 
hard  tissues  and  serve  to  maintain  their  rigidity.  These 
salts  are  taken  into  the  body  as  such,  and  are  eliminated 
with  the  urine,  sweat,  and  faeces. 

The  carbonates  are  found  in  the  same  tissues  as  the  phos- 
phates, and  they  also  serve  the  same  purpose.  The  salts 
of  this  class  predominate  in  the  herbivora,  whereas  in  the 
carnivora  the  phosphates  are  the  more  numerous. 

The  other  salts  mentioned  as  existing  in  the  body  are 
more  incidental.  They  are  found  in  the  tissues,  fluids, 
and  secretions,  and  are  sometimes  taken  in  as  such  with 
the  food  and  drink,  and  sometimes  are  the  result  of  chemi- 
cal processes  within  the  body. 

3.  Inorganic  acid.  In  the  human  organism  hydrochloric 
acid  is  found  in  a  free  state  in  the  gastric  juice. 

4.  The  gases.  In  a  previous  lecture  I  stated  that  certain 
gases — namely,  oxygen,  nitrogen,  and  carbon  dioxide — 
exist  in  the  blood.  Besides  this  we  find  CH„  NH3,  and 
H5S,  traces  of  which  are  absorbed  from  the  intestinal  tract, 
in  which  they  form  as  a  result  of  the  decomposition  of  the 
food  residue. 

5.  The  metals  existing  as  such  in  the  body  are  iron,  man- 
ganese, and  aluminum.  In  the  liver  and  bile  traces  of 
copper,  together  with  the  other  metals  mentioned,  have 
also  been  found.  They  often  form  ingredients  of  certain 
bile  stones.  Iron  constitutes  0.42  per  cent  of  the  haemo- 
globin of  the  blood. 

II.    THE   ORGANIC   PROXIMATE   PRINCIPLES. 

The  substances  of  this  group  are  chemical  compounds 


CHEMICAL   INGREDIENTS   OF   THE   HUMAN   ORGANISM,         63 

which  originate  and  exist  only  in  living  organisms.  These 
substances  do  not  originate  or  exist  in  the  inorganic  world. 

The  vegetable  organism  is  capable  of  producing  organic 
substances  from  inorganic  material.  The  plants  take  from 
the  soil,  air,  and  water,  inorganic  material,  and  transform 
it  into  the  organic  material  composing  their  tissues. 

The  animal  organism  must  receive  for  its  nutrition  or- 
ganic material  already  formed  in  other  organisms,  in  order 
to  be  able  to  form  and  reproduce  its  own  organic  material. 
The  animal  organism,  therefore,  is  not  capable  of  produc- 
ing organic  substances  from  inorganic  material. 

The  organic  proximate  principles  are  divided  into  (1)  or- 
ganic non-nitrogeuized  and  (2)  organic  nitrogenized  sub- 
stances. 

1.  Tlie  Organic  Xon-nitrogenized  Proximate  Principles. 

The  members  of  this  class  are  composed  of  oxygen, 
hydrogen,  and  carbon,  united  in  varying  proportions  to 
form  compounds  which  have  a  simple  chemical  constitu- 
tion. 

They  are  again  subdivided  into  two  groups— namely,  into 
(a)  carbohydrates  and  (b)  hydrocarboncdes. 

(a)  The  Carbohydrates. — The  members  of  this  group  are 
distinguished  from  those  of  the  second  group  in  that  the 
hydrogen  and  oxygen  are  always  present  in  them  in  the 
proportion  in  which  they  are  found  in  water.  This  group 
includes  the  starches  and  sugars. 

The  carbohydrates  of  the  plants  are  formed  within  these 
from  inorganic  material,  and  the  first  organic  substance  so 
formed  is  starch,  from  which  all  other  organic  compounds 
of  plants  are  finally  developed. 

The  green  plants — namely,  those  containing  chlorophyll 
(the  green  coloring  matter  of  the  plants) — are  capable,  under 
the  influence  of  solar  light,  of  taking  up  carbonic  dioxide 
from  the  air,  and  water  from  the  soil,  and  transforming 
them  into  starch;  during  this  process  oxygen  is  liberated 


64       LECTURES   ON  HUMAN   PHYSIOLOGY  AND  HISTOLOGY. 

and  exhaled  by  the  plant.    The  process  can  be  expressed" 
by  a  chemical  equation  as  follows: 

6C0.  +  5H.0  =  CeH.oOB  +  0,2. 

Starch  is  contained  in  many  plants  used  as  food — for 
example,  in  wheat,  rye,  oats,  barley,  rice,  corn,  peas, 
beans,  potatoes,  etc. 

Plants  containing  a  large  percentage  of  carbohydrate 
material  are  called  amylaceous  plants.  The  starch  is  con- 
tained in  the  plants  in  the  form  of  granules.  Starch  gran- 
ules consist  of  a  substance  called  granulose,  embedded  in  a 
dense,  firm  substance,  the  cellulose.  Granulose  is  soluble,, 
cellulose  is  insoluble,  in  water. 

The  chemical  formula  for  starch  is  CeHjoO^;  with  iodine 
it  forms  a  chemical  compound,  the  iodide  of  starch;  this 
has  an  indigo-blue  color  and  is  readily  formed  when  iodine 
comes  in  contact  with  starch;  iodine  is,  for  this  reason, 
used  as  a  test  to  detect  the  presence  of  starch. 

All  organic  substances  in  plants  are  the  result  of  chemi- 
cal changes  which  take  place  under  the  varying  conditions 
of  temperature,  climate,  and  soil. 

The  carbohydrate  substances  existing  in  the  animal  body 
are  formed  mainly  from  carbohydrate  material  taken  in  as 
such  with  the  food.  The  carbohydrates  found  in  the  fluids 
and  tissues  of  the  human  body  are  dextrin,  glycogen,  glu- 
cose, and  lactose  or  inosit.  Dextrin  is  a  carbohydrate  sub- 
stance which  is  formed  in  the  alimentary  canal  as  the 
result  of  the  action  of  the  so-called  diastatic  ferments  of 
the  digestive  juices  upon  starchy  foods.  Dextrin  is  a 
substance  isomeric  with  starch — that  is,  it  has  the  same 
chemical  formula,  but  differs  in  its  physical  properties.  It 
has  a  brownish  color  and  is  soluble  in  water;  with  iodine 
it  gives  a  rose-red  color.  Dextrin  can  be  formed  from 
starch  by  heating,  by  the  addition  of  dilute  sulphuric  acid, 
and  by  the  addition  of  diastatic  ferments — namely,  the  dias- 
tase of  plants  and  the  diastatic  ferments  of  the  animal 


CHEMICAL   INGREDIENTS   OF   THE   HUMAN   ORGANISM.       65 

digestive  juices.  Glycogen  is  a  carbohydrate  substance 
which  is  isomeric  with  starch  and  dextrin.  It  has  the 
same  chemical  composition  as  these — namely,  CeHioO, — but 
differs  in  its  physical  properties;  it  is  soluble  in  water; 
with  iodine  it  gives  a  dark-brownish  color.  Glycogen  is 
also  called  animal  starch;  it  is  produced  in  the  liver  by 
a  process  of  dehydration  of  glucose.  Glucose,  also  called 
dextrose  or  grcqDC- sugar,  is  that  variety  of  sugar  which  is 
found  in  ripe  grapes  and  in  the  juices  of  many  sweet  fruits 
and  flowers;  also,  to  some  extent,  in  honey.  In  the  animal 
body  small  portions  of  this  are  found  in  the  blood,  muscle- 
tissue,  liver,  chyle,  and  urine.  Glucose  in  the  animal  body 
is  the  result  of  the  continued  action  of  diastatic  ferments 
upon  carbohydrate  foods.  In  plants  glucose  is  formed 
from  starch  under  the  influence  of  climate  and  solar  heat; 
it  can  be  produced  artificially  by  boihng  starch  with  dilute 
sulphuric  acid.  The  transformation  of  starch  into  glucose 
consists  in  the  assumption  of  one  molecule  of  water.  The 
process  may  be  expressed  by  the  following  chemical  equa- 
tion: 

CeHioOolstarcli)  +  HaOCwater)  =  CsHioOg  (glucose). 

In  a  disease  called  diabetes  mellitus  the  production  of  this 
variety  of  sugar  in  the  animal  body  is  so  excessive  that  the 
sugar  is  eliminated  with  the  urine.  Constant  symptoms 
of  this  disease  are  great  thirst  and  great  desire  to  eat;  pass- 
ing of  large  quantities,  often  gallons,  of  urine  daily;  ema- 
ciation, dry  and  itching  skin,  and  the  appearance  of  pecu- 
liar skin  eruptions  and  ulcers.  A  positive  diagnosis  is 
made  by  an  analysis  of  the  urine,  and  in  order  to  make 
such  analysis  it  is  essential  to  be  familiar  with  the  more 
common  tests  and  to  determine  the  presence  of  glucose. 
The  tests  most  frequently  used  are  the  alkali  test,  Trom- 
mer's  test,  and  the  fermentation  test. 

The  alkali  test  used  to  determine  the  presence  of  glucose 
is  as  follows  :  To  the  suspected  solution  a  few  drops  of 
a  solution  of  potassium  hydrate  are  added  and  the  whole 


66       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

heated;  the  presence  of  glucose  is  indicated  by  a  brown 
color.  This  test,  however,  is  not  positive,  because  other 
incidental  ingredients  of  urine  give  a  similar  reaction. 

Trommels  test  for  the  determination  of  the  presence  of 
sugar  is  as  follows:  To  the  suspected  solution  first  an  al- 
kaline solution,  such  as  sodium  hydrate,  is  added  to  render 
it  alkaline,  then  a  few  drops  of  a  solution  of  cupric  sul- 
phate are  added,  and  the  whole  is  now  heated;  if  glucose 
is  present  a  red  color  will  quickly  be  produced,  and,  on 
standing,  a  brick-red  precipitate  will  form.  This  test  is 
based  upon  a  quality  of  the  glucose  which  consists  in  its 
power  to  reduce  certain  metallic  compounds  under  favor- 
able conditions.  In  this  test  the  soluble  cupric  sulphate 
is  reduced  to  a  suboxide  of  copper,  which  is  a  brick-red  in- 
soluble powder.  The  solutions  used  for  this  test,  as  pre- 
scribed by  Fehling,  are  as  follows : 

(a)  The  alkaline  solution:  150  grammes  of  potassium 
tartrate  are  dissolved  in  500  cubic  centimetres  of  a  10  per 
cent  solution  of  sodium  hydrate. 

(6)  The  sulphate  of  copper  solution:  S-t.a  grammes  of 
cupric  sulphate  are  dissolved  in  200  cubic  centimetres  of 
distilled  water.  These  two  solutions  are  mixed,  and  dis- 
tilled water  is  added  to  make  1,000  cubic  centimetres. 
One  cubic  centimetre  of  this  solution  contains  a  quantity 
of  cupric  sulphate,  which  is  reduced  to  a  suboxide  of  cop- 
per by  0.0005  of  sugar.  With  this  solution  it  is  possible, 
therefore,  to  make  a  qualitative,  and  also  approximately 
a  quantitative,  examination  for  sugar. 

The  fermentation  test  is  based  upon  the  fact  that  glucose 
is  decomposed  into  carbon  dioxide  and  alcohol  by  yeast,  a 
vegetable  ferment.  If  to  a  fluid  containing  glucose,  yeast 
is  added,  bubbles  of  gas  will  soon  be  seen  to  rise  from  the 
surface  of  the  fluid  ;  this  gas  is  carbon  dioxide.  The  little 
apparatus  used  for  this  purpose  is  so  arranged  that  the  gas 
is  collected  in  the  upper  closed  portion  of  the  glass  tube, 


CHEMICAL  INGREDIENTS   OF   THE   HUMAN   ORGANISM.       67 

^nd  from  the  quantity  so  collected  in  a  certain  time  the 
quantity  of  glucose  can  be  calculated, 

Levulose,  or  inverted  sugar,  is  found  in  the  alimentary 
canal,  where  it  is  formed  by  the  action  upon  carbohydrate 
foods  of  a  ferment  of  the  succus  entericus,  called  invertin. 
It  also  exists  as  such  in  the  juice  of  many  fruits.  It  is 
isomeric  with  glucose  and  rotates  the  rays  of  polarization 
toward  the  left.  It  rarely  occurs  in  the  urine  in  diseased 
conditions. 

Lactose,  or  milk-sugar,  is  an  important  constituent  of 
mother's  milk.  Its  chemical  formula  is  Ci^Ho^Oi^.  It  is 
not  as  sweet  and  not  as  soluble  as  glucose,  but  it  responds 
to  the  same  tests.  It  is  found  in  the  urine  of  nursing- 
mothers,  being  absorbed  from  the  excess  of  milk  in  the 
mammary  glands.  During  its  fermentation  lactic  acid  is 
formed. 

Inosit  is  a  sugar  contained  in  muscle  and  in  many  other 
tissues  of  the  body ;  it  is  also  contained  in  plants,  princi- 
pally in  the  leguminous  plants,  such  as  beans. 

Inosit,  CeHioOe,  is  insoluble  in  alcohol,  has  a  sweet  taste, 
and  does  not  respond  to  the  tests  generally  applied  to 
glucose. 

In  pathological  conditions  it  occurs  in  the  urine  and  the 
fluid  of  echinococcus  cysts,  together  with  glucose. 

The  carbohydrate  substances  in  the  body  are  tissue-form- 
ing and  heat-producing  materials  ;  they  are  eliminated 
from  the  body,  not  in  their  own  form,  but  after  undergoing 
processes  of  decomposition. 

(&)  Tim  Hydrocarhonates. — The  members  of  this  group 
contain  carbon  in  abundance,  and  hydrogen  and  oxygen 
not  in  a  proportion  to  form  water.  To  this  class  belong 
the  fats  and  oils  and  the  fatty  acids.  The  fats  and  oils 
existing  in  the  human  body  are  the  palmitin,  stearin,  olein, 
butyrin,  caprolin,  caprylin,  caprinin,  myristin,  and  choles- 
terin. 


68       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Olein,  palmitin,  and  stearin  are  the  substances  consti- 
tuting the  fat  of  the  animal  body  ;  they  also  exist  in  many 
fruits  and  nuts.  They  are  insoluble  in  water,  freely  solu- 
ble in  ether.  At  ordinary  temperatures  olein  is  liquid,  pal- 
mitin  and  stearin  solid.  In  the  animal  body  they  are 
always  combined  and  exist  in  a  liquid  form  ;  palmitin  and 
stearin  solidify  after  death. 

Butyrin,  caproliri,  caiwylin,  caprinin,  and  myiHstin 
exist  in  the  milk  and  constitute  the  fatty  substances  of 
butter.  Cholesterin  is  a  substance  belonging  to  this  class; 
it  exists  in  small  amounts  in  the  blood,  bile,  and  in  many 
other  tissues  ;  it  constitutes  a  great  part  of  the  so  called 
gall-stones. 

The  fatty  acids  are:  1,  oleic;  2,  stearic;  3,  palmitic;  4, 
butyric;  5,  caproic;  6,  capric;  7,  formic;  8,  acetic;  9,  pro- 
pionic ;  10,  sebacic ;  11,  leucic ;  12,  lactic ;  13,  oxalic ;  14^ 
benzoic;  15,  carbolic. 

Of  these,  numbers  1  to  6  are  found  in  small  quantities  in 
the  alimentary  canal  as  the  result  of  the  breaking-up  of  the 
fats  into  glycerin  and  fatty  acids  in  the  presence  of  certain 
ferments.  The  fatty  acids  unite  with  alkalies  to  form  soap. 
Numbers  7  to  11  inclusive  are  present  in  sweat  and  in  the 
fatty  secretions  of  the  skin. 

Lactic  acid  exists  in  the  juice  of  the  muscle-tissue,  and 
at  times  it  is  found  as  a  product  of  decomposition  in  the 
alimentary  canal. 

Oxalates  are  found  in  the  urine  after  the  taking  of  cer- 
tain foods  and  drinks. 

Traces  of  benzoic  and  carbolic  acid  (the  so-called  aromatic 
acids)  are  sometimes  found  in  urine. 

The  hydrocarbonates  in  the  animal  body  are,  like  the 
carbohydrates,  tissue-forming  and  heat-producing  sub- 
stances. They  are  eliminated  only  to  a  small  extent  as 
such  with  the  excretions,  viz.,  with  the  sweat,  urine,  and 
faeces  ;  the  greater  number  of  these  substances  undergo 
chemical  changes  in  the  body. 


LECTUEE  X. 

THE   CHEMICAL   INGREDIENTS   OF   THE   HUMAN   ORGANISM 

{continued). 

In  my  last  lecture  I  finished  the  description  of  those 
organic  ingredients  of  the  animal  body  which  contain  no 
nitrogen.  To-day  I  will  take  up  those  which  contain  nitro- 
gen.    They  are  known  as  the 

2.   Organic  Nitrogenizecl  Proximate  Principles. 

The  following  substances  belong  to  this  class:  (a)  the 
albuminous  substances  ;  ih)  the  albuminoid  substances  ; 
(c)  the  ferments;  (cZ)  the  coloring  substances;  (e)  the  pro- 
ducts of  the  decomposition  of  the  albuminous  and  albu- 
minoid substances  in  the  animal  body. 

(a)  The  Albuminous  Substances. 

The  substances  of  this  class  are  also  called  the  proteins. 
They  are  composed  of  carbon,  oxygen,  hydrogen,  nitrogen, 
and  sulphur.  They  constitute  the  main  portion  of  the  pro- 
toplasm of  the  tissues  and  are  introduced  into  the  body 
with  the  food.  These  substances  originate  in  the  plants 
and  develop  in  them  from  non-nitrogenous  matter  by  the 
taking  up  of  sulphur  and  nitrogen  from  the  sulphates  and 
nitrates  of  the  soil. 

The  exact  chemical  composition  of  the  albuminous  sub- 
stances is  unknown.  The  elements  composing  them  exist 
in  the  following  approximate  proportions:  carbon,  49  to  54 
per  cent;  oxygen,  20  to  23  per  cent;  hydrogen,  6  to  7  per 
cent;  nitrogen,  14  to  17  per  cent;  sulphur,  0.8  to  2  per  cent. 

The  albuminous  substances  have  in  common  certain 
characteristic  properties.     They  are  all  non-crystallizable, 


70       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

non-diffusible,  coagiilable,  putrefactive,  hygroscopic,  and 
they  all  undergo  catalytic  transformations  in  the  presence 
of  ferments. 

Albuminous  substances  are  soluble  in  strong  acids  and 
alkalies,  but  also  undergo  chemical  changes.  Some  are 
soluble  in  water,  saline  solutions,  and  in  dilute  acids  or 
alkalies.  Most  of  them  are  insoluble  in  alcohol  and  ether.. 
These  substances  can  rarely  be  obtained  in  a  pure  state, 
but  can  be  precipitated  from  their  solutions  in  an  amor- 
phous condition. 

The  chemical  reactions  generally  employed  as  tests  for 
albuminous  substances  are: 

1.  The  Xantho-proteic  Reaction. — When  albuminous 
substances  are  coagulated  by  the  addition  of  nitric  acid, 
and  heat  is  applied,  a  yellowish  color  is  produced,  which, 
upon  the  addition  of  ammonia,  becomes  a  dark-orange 
color. 

2.  Milloii's  Reaction. — When  to  a  solution  containing 
albuminous  substances  Millon's  reagent  (a  solution  of 
nitrites  and  nitrates  of  mercury)  is  added  and  the  solution 
is  then  heated,  a  reddish -pink  color  is  produced. 

3.  When  to  a  solution  containing  albuminous  matter 
ferrocyanide  of  potassium  and  acetic  acid  are  added,  a 
white  precipitate  is  formed;  the  same  result  is  obtained 
when  the  solution  is  boiled  with  acetic  acid  and  sodium 
sulphate. 

4.  When  a  solution  containing  albuminous  matter  is 
boiled  with  potassium  hydrate  and  a  little  of  a  cupric  sul- 
phate solution  is  added,  a  deep  purple  color  is  produced, 

5.  When  treated  with  iodine,  albuminous  substances  as- 
sume a  yellow-brown  color. 

The  albuminous  substances  are  divided  iuto  the  following 
groups  :  the  true  albumins,  the  derived  albumins,  the  glo- 
bulins, the  peptones  and  albuminoses. 

The  true  allmmius  are  the  egg  albumin  and  the  serum- 
albumin.     The  latter  is  contained  in  the  blood,  lymph,  and 


Cd:EM;[CAL   IN^GREDIENT   OF   THE   HUMAN   ORGANISM.  7L 

chyle,  in  the  synovial  and  serous  fluids,  and  in  the  paren- 
chymatous juice  of  the  tissues.  In  certain  physiological 
and  in  many  pathological  conditions  it  is  found  in  the  urine. 

The  derived  albumins  are  the  acid-  and  alkali-albumins. 
Both  are  formed  when  albuminous  substances  come  in 
contact  with  acids  or  alkalies  respectively.  In  the  ani- 
mal body  they  are  formed  in  the  alimentary  canal  during 
digestion,  by  the  presence  of  the  acid  or  alkaline  digestive 
juices. 

Syntonin  is  an  albuminous  substance  resembling  acid- 
albumin;  it  is  found  in  muscle-tissue. 

Alkali  albumins  are  also  termed  albuminates. 

The  globulins  are  the  globulin  or  crystallin  of  the  lens 
of  the  eye,  the  myosin  contained  in  muscle-tissue,  the 
serum-globulin,  the  fibrinogen  contained  in  the  blood,  and 
the  casein  contained  in  the  milk.  These  substances  are 
insoluble  in  water,  but  soluble  in  weak  saline  solutions. 

Tlie  peijtones  and  albuminoses.  The  peptones  are  formed 
by  the  action  of  the  digestive  juices  in  the  alimentary 
canal  upon  albuminous  and  albuminoid  substances  ;  the 
change  they  undergo  renders  them  diffusible. 

Besides  the  tests  already  mentioned,  the  so-called  Biuret 
reaction  is  used  to  detect  the  presence  of  peptones.  This 
consists  in  the  addition  to  the  suspected  solution  of  a 
solution  of  cupric  sulphate  and  potassium  hydrate;  heat  is 
applied,  and  a  reddish  discoloration  indicates  the  presence 
of  peptones. 

Albuminoses  are  the  intermediate  products  of  the  change 
of  albuminous  and  albuminoid  substances  into  peptones. 
Albuminoses  are  also  termed  proj^ejjtones. 

(6)  The  Albuminoid  Substances. 

The  substances  of  this  class  resemble  the  albuminous 
substances  as  regards  their  chemical  composition ;  not  all 
of  them  contain  sulphur.  They  possess  the  same  general 
chemical  properties,  and  the  products  of  their  decomposi- 


72       LECTURES   ON   HUMAN  PHYSIOLOGY    AND   HISTOLOGY. 

tion  resemble  those  of  the  decomposition  of  albuminous 
substances.  It  is  believed  that  these  are  formed  from  the 
albuminous  materials  by  a  synthetical  process.  The  albu- 
minoid materials  probably  do  not  possess  the  same  physio- 
logical value  as  the  albuminous  materials.  They  exist  in 
the  animal  body  in  a  liquid,  solid,  or  semi-solid  form,  and 
constitute  the  basis  of  many  tissues,  such  as  the  connective 
tissues,  the  bones,  nails,  hair,  mucous  membranes,  etc. 

The  substances  belonging  to  this  group  are:  CaUogen, 
contained  in  the  bones,  tendons,  ligaments,  cartilages,  etc. 
When  boiled  it  yields  glue. 

Chondrin,  contained  in  the  cartilages;  on  boiling,  it  also 
yields  a  gelatinous  substance. 

Elastin,  contained  in  elastic  tissue. 

Keratin  is  the  substance  which  is  obtained  when  horny 
tissues — such  as  nails,  hair,  and  epidermis — are  treated  with 
substances  which  extract  the  other  soluble  materials  from 
these  tissues. 

Mucin  is  contained  in  the  mucous  and  other  slimy  secre- 
tions. 

The  protonuclein,  which  forms  the  larger  portions  of  the 
cell-nuclei,  is  also  classed  in  this  group;  it  is  an  organic 
nitrogenous  substance  containing  phosphorus. 

Hcemoglohin,  the  coloring  matter  of  the  blood,  is  also  to 
be  considered  an  albuminoid  substance;  it  is  composed  of 
albumin  and  haematin. 

(c)  The  Ferments. 

Ferments  are  substances  which  produce  chemical  changes 
in  other  substances  with  which  they  come  in  contact.  They 
are  divided  into  the  organized  and  into  the  non-organized 
ferments. 

The  non-orgayiized  ferments,  or  enzymes,  are  those  which 
by  their  mere  presence  produce  changes  in  other  sub- 
stances without  undergoing  any  changes  themselves.  Very 
small  amounts  are  capable  of  producing  these  changes  in 
large  quantities  of  other  substances.    Temperature  infiu- 


CHEMICAL  INGREDIENTS   OP   THE   HUMAN   ORGANISM.         73 

ences  this  peculiar  property  in  such  a  manner  that  cold  and 
heat  retard  and  destroy  it,  whereas  a  medium  temperature 
is  most  favorable  to  it.  The  enzymes  have  an  unknown 
chemical  constitution,  but  resemble  the  albuminoids  in 
their  combination;  they  do  not  respond  to  the  same  chemi- 
cal tests  as  these. 

The  unorganized  ferments,  or  enzymes,  existing  in  the 
animal  body  are: 

1.  The  amylolytic  ferments  are  those  which  produce 
changes  in  carbohydrate  substances.  These  are  :  the  j^tya- 
lin  of  the  saliva,  the  amylopsin  of  the  pancreatic  juice, 
the  invertin  of  the  intestinal  juice.  In  the  blood,  lymph, 
chyle,  milk,  urine,  and  in  the  liver,  traces  of  an  amylolytic 
or  diastatic  ferment  exist. 

2.  The  proteolytic  ferments  are  those  which  produce 
changes  in  albuminous  and  albuminoid  substances.  These 
are  i\\e,  pepsin  of  the  gastric  juice,  the  tryp)sin  of  the  pan- 
creatic juice,  a  proteolytic  ferment  of  the  intestinal  juice. 

3.  Ferments  acting  upon  fats,  the  steapsin  of  the  pan- 
creatic juice. 

4.  Milk-curdling  ferments,  existing  in  the  gastric  juice, 
pancreatic  juice,  and,  in  traces,  in  the  urine. 

5.  The  fibrin-ferment,  existing  in  the  blood,  plasma, 
lymph,  and  serous  fluids. 

The  organized  ferments  are  not  constituents  of  the  ani- 
mal body,  but  they  are  taken  in  with  the  food  and  drink. 
In  the  alimentary  canal  they  take  part  in  many  of  the 
chemical  processes.  The  organized  ferments  are  vegetable 
micro-organisms  or  bacteria.     To  this  class  belong: 

The  hacterium  lactis,  which  decomposes  sugar  into  lactic 
acid,  etc. 

The  saccharomyces,  which  decompose  sugar  into  alcohol 
and  carbon  dioxide. 

The  bacteria  of  putrefaction,  which  are  principally  found 
in  the  lower  part  of  the  intestinal  canal,  where  they  cause 
a  decomposition  of  substances  and  the  production  of  fetid 
;gases.    Besides  these,  certain  bacteria  find  entrance  into  the 


74       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

animal  body,  which,  by  their  presence,  produce  pathologi- 
cal conditions.     These  are  known  as  j)citJiogenic  bacteria. 

(d)  The  Coloring  Matters. 

The  substa.nces  of  this  class  are  nitrogenous.  They  are 
considered  to  be  derivatives  of  the  albuminous  and  albu- 
minoid materials  of  the  body.  They  are,  almost  all  of  them, 
crystallizable;  a  few  of  them  can  be  obtained  only  in  an 
amorphous  condition.  These  substances  are  contained  in 
many  fluids  and  tissues  of  the  body,  partly  in  solution, 
partly  deposited  in  the  form  of  amorphous  granules  in  the 
cells  of  the  tissues. 

The  coloring  matters  existing  in  the  human  body  are : 

1.  The  coloring  matter  of  the  blood — viz.,  the  hwmo- 
glohin.  * 

2.  The  coloring  matters  of  the  l:>ile — the  bilirnbi)/,  the 
biliverdin,  the  biliprasin. 

3.  The  coloring  matters  of  the  urine — urochnmie,  nro- 
bilin,  indigo  blue. 

4.  The  pigments  of  the  skin,  iris,  choroid,  hair,  and  epi- 
dermis— the  melanin. 

(e)  The  Products  of  the  Decomposition  and  Disintegration  of 

THE   ALBUMrNOUS  AND  ALBUMINOID  SUBSTANCES. 

The  substances  of  this  class  are  derivatives  of  NH3,  result- 
ing from  the  dissimilating  metamorphosis  of  the  albumin- 
ous and  albuminoid  substances.  These  products  belong  tO' 
the  group  of  chemicals  known  as  amines  and  amides. 

Amines  are  those  substances  in  which  atoms  of  the  H  of 
the  NH3  molecule  are  replaced  by  alcohol  radicals. 

Amides  are  those  in  which  atoms  of  the  H  in  the  NH^ 
molecule  are  replaced  by  an  acid  radical. 

The  substances  belonging  to  this  class  are:  Lencin,  found 
in  the  tissues  of  many  organs,  as  in  the  brain,  lungs,  liver, 
etc.  It  is  also  formed  in  the  alimentary  canal  during  the 
pancreatic  digestion. 


CHEMICAL  INGREDIENTS   OF   THE   HUMAN   ORGANISM.        75 

Tyrosin  is  always  found  in  company  with  leucin;  it  is 
also  formed  during  the  pancreatic  digestion. 

Glycocoll,  glycin  or  amido-acetic  acid,  is  not  found  free 
in  the  animal  body,  but  exists  in  the  glycocholic  acid  of  the 
bile  and  in  the  hippuric  acid  of  the  urine. 

Kreatin  or  kreatinin.  Kreatin  is  found  principally  in 
the  juice  of  the  muscles,  but  also  in  many  other  fluids  of 
the  body.     Kreatinin  exists  in  the  urine. 

Taurin  is  formed  as  a  product  of  the  decomposition  of 
taurocholic  acid;  it  is  found  in  small  quantities  in  the 
lungs,  muscles,  and  kidneys. 

Xanthin  and  hypoxanthin  are  contained  in  small  quanti- 
ties in  the  lungs,  spleen,  and  in  other  tissues. 

Uric  acid  is  contained  principally  in  the  urine,  generally 
in  combination  in  the  form  of  salts. 

Hippuric  acid  is  found  in  small  quantities  in  human 
urine,  in  larger  amounts  in  that  of  horses. 

Urea  is  the  main  organic  ingredient  of  human  urine;  it 
is  also  found  in  small  quantities  in  the  blood  and  the  lymph. 
Urea  is  the  final  product  of  the  decomposition  of  the 
albuminous  and  albuminoid  substances. 

Indol  and  skatol  are  two  malodorous  products  of  the 
putrefaction  of  albuminous  and  albuminoid  substances  in 
the  intestinal  canal. 

Lecithin,  protagon,  neurin,  and  cerebrin  are  those  nitro- 
genous substances  which  are  not  found  as  such  in  the  ex- 
cretions, but  are  believed  to  be  products  of  the  disinte- 
gration of  albuminous  and  albuminoid  substances  in  the 
body.  Lecithin,  protagon,  neurin,  and  cerebrin  are  con- 
tained principally  in  the  substance  of  the  brain  and  nerve 
tissue.  They  all,  with  the  exception  of  cerebrin,  contain 
phosphorus. 

Besides  the  substances  of  this  class  above  enumerated, 
there  are  probably  many  others  which  are  merely  interme- 
diate products  of  the  final  decomposition  and  splitting-up 
of  the  albuminous  and  albuminoid  substances  in  the  body. 


76      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

In  my  description  of  the  chemical  ingredients  of  the 
human  body,  I  have  dwelt  only  in  a  general  way  on  their 
physical  and  chemical  properties. 

I  have  avoided  dwelling  at  length  on  these  points,  that  I 
might  not  conflict  with  the  instruction  which  you  will  re- 
ceive from  your  professor  of  chemistry  in  the  course  in 
physiological  chemistry  which  forms  part  of  the  curricu- 
lum of  the  senior  year.  A  practical  demonstration  of  these 
substances,  together  with  a  practical  study  of  their  chemi- 
cal and  physical  properties,  will  certainly  aid  you  more 
than  mere  theoretical  description. 

With  this  my  tenth  lecture,  ladies  and  gentlemen,  I 
finish  with  the  subjects  a  study  of  which  I  consider  essen- 
tial as  introductory  to  physiology,  A  study  of  the  his- 
tology of  the  elementary  tissues  and  their  physiological 
properties  is  essential  for  the  study  of  the  organs  of  the 
body  and  their  physiology.  As  most  physiological  pro- 
cesses are  due  to  chemical  and  physical  changes,  it  is 
necessary  to  know  the  ingredients  of  the  animal  body  and 
their  chemical  relations. 

For  the  purpose  of  a  better  understanding  I  have  drawn 
up  the  following  schedule  of  the  classification  of  the  proxi- 
mate principles  which  I  have  adopted  : 

I.  Inorganic  substances. 

1.  Water. 

2.  Inorganic  salts. 

Chlorides  of  sodium  and  potassium. 

Phosphates  of  sodium,  potassium,  and  magnesium. 

Carbonates  of  sodium,  potassium,  and  magnesium. 

Sulphates  of  sodium  and  potassium. 

Chloride  of  calcium. 

Carbonate  of  calcium. 

Chloride  of  ammonium. 

Bicarbonate  of  sodium. 


CHEMICAL   INGREDIENTS   OF   THE   HUMAN   ORGANISM. 


77 


3.  Inorganic  acids. 

Hydrochloric  acid. 

4.  Gases. 

0,  N,  C0„  CH„  NH„  H,S. 

5.  Metals. 

Iron,  Aluminium,  Copper  (Lead  ?) 

II.  Organic  substances. 

(A)  Non-nitrogenous. 
(a)  The  carbohydrates. 

1.  Dextrin. 

2.  Glucose. 

3.  Glycogen. 

4.  Levulose. 

5.  Lactose. 

6.  Inosit. 

(6)  The  hydrocarbonates. 

1.  Fats  and  oils. 

Butyrin,  Olein, 

Caprolin,  Palmitin, 

Caprylin,  Stearin, 

2.  Fatty  acids. 

Oleic  acid,         Capric  acid. 
Stearic  acid,     Formic  acid. 
Palmitic  acid.  Acetic  acid. 
Butyric  acid.    Propionic  acid, 
Caproic  acid,   Sebacic  acid, 

(B)  Nitrogenous. 

{a)  Albuminous  substances. 

1.  The  true  albumins. 

Egg-albumin. 
Serum-albumin. 

2.  Derived  albumins. 

Acid  albumins. 
Syntonin. 
Alkali-albumins. 
Casein. 


Caprinin, 
Myristin, 
Cholesterin. 

Lactic  acid, 
Leucic  acid, 
Oxalic  acid. 
Benzoic  acid, 
Carbolic  acid. 


78       LECTURES   ON   HUMAN  PHYSIOLOGY   AND    HISTOLOGY. 

3.  Globulins. 

Globulin  of  crystalline  lens. 

Serum-globulin. 

Fibrinogen. 

Myosin, 
■i.  Peptones  and  albuminoses. 
(6)  Albuminoid  substances. 

Callogen. 

Elastin. 

Keratin. 

Mucin. 

Protonuclein. 

Haemoglobin. 

(c)  Ferments. 

1.  Unorganized  ferments. 

Amylopsin. 

Ptyalin. 

Pepsin. 

Trypsin. 

Steapsin. 

Invertin. 

Milk-curdling  ferment. 

Fibrin-ferment. 

2.  Organized  ferments. 

Bacteria. 
Bacterium  lactis. 
Saccharomy  ces. 
Putrefactive  bacteria. 
Pathogenic  bacteria. 

(d)  The  coloring  matters. 

Haemoglobin. 
Bile-coloring  matters. 
Urine- coloring  matters. 
Melanin. 


CHEMICAL   INGREDIENTS    OF   THE   HUMAN   ORGANISM.       79 

(e)  Decomposition  products. 
Leucin. 
Tyrosin. 
Glycin. 

Kreatin  and  kreatinin. 
Xanthin  and  hypoxanthin. 
Uric  acid. 
Hippuric  acid. 
Urea. 

Indol  and  skatol. 
Lecithin,  protagon,  neurin,  and  cerebrin. 


QUESTIONS   AND   ANSWERS. 

Subject. — The  Proximate  Principles. 
Lectures  IX.-X.  inclusive. 

146.  Name  the  chemical  elements  which  enter  into  the 
chemical  composition  of  the  animal  body. 

147.  Which  of  these  exist  in  the  body  in  a  free  state  ? 

148.  What  is  a  proximate  principle  i 

149.  Name  the  inorganic  ingredients  of  the  animal  body. 

150.  What  is  the  proportion  of  water  in  the  animal  body  ? 

151.  What  percentage   of   water  is  contained  in  blood, 
bone,  enamel  i 

152.  Enumerate  the  inorganic  salts  in  the  animal  body. 

153.  What  are  the  uses  of  the  chlorides  in  the  body  ? 

154.  Where  are  the  sulphates  principally  found  ? 

155.  Where  are  the  phosphates,  the  carbonates,  and  the 
calcium  salts  principally  found  ? 

156.  Name  the  inorganic  acid  existing  as  such  in   the 
human  body.     State  where  found. 

157.  Name  the  gases  existing  as  such  in  the  animal  body. 
State  where  they  are  found. 


80      LECTURES   ON    HUMAN    PHYSIOLOGY    AND    HISTOLOGY. 

158.  Name  the  metals  existing  in  the  animal  body. 
State  where  they  exist. 

159.  Where  do  the  animal  inorganic  ingredients  origi- 
nate, how  are  they  taken  into  the  body,  and  how  are  they 
eliminated  ? 

160.  Give  a  short  classification  of  the  organic  ingredients 
of  the  animal  body. 

161.  How  do  the  organic  ingredients  of  the  animal  body 
originate,  and  where  ? 

162.  What  do  you  understand  by  carbohydrate  substan- 
ces ? 

163.  Name  the  carbohydrate  substances  existing  in  the 
human  body.     State  where  they  exist. 

164.  Give  chemical  tests  for  starch,  dextrin,  glucose. 

165.  What  do  you  understand  by  hydrocarbonate  sub- 
stances ? 

166.  Mention  the  hydrocarbonate  substances  existing  in 
the  animal  body. 

167.  In  what  form  are  the  carbohydrates  and  hydrocar- 
bonates  eliminated  from  the  body  ? 

168.  What  do  you  understand  by  organic  nitrogenous 
substances  ? 

169.  What  substances  of  our  body  belong  to  this  class  ? 

170.  Which  are  the  albuminous  substances  in  the  animal 
body  ? 

171.  Give  the  general  properties  of  the  albuminous  sub- 
stances. 

172.  Mention  and  describe  the  tests  used  for  the  albu- 
minous substances. 

173.  Name  the  native  albumins,  the  derived  albumins, 
and  the  globulins. 

174.  What  are  the  peptones,  and  what  are  propeptones 
or  albuminoses  ? 

175.  What  are  the  albuminoid  substances  ?  Enumerate 
them. 

176.  What  is  a  ferment  ? 


QUESTIONS   AND   EXERCISES.  81 

177.  Which  are  the  unorganized  ferments  or  enzymes 
existing  in  the  human  body  ?   State  where  they  are  found. 

178.  What  is  a  hydrolytic,  a  proteolytic,  and  an  amylo- 
lytic  ferment  ? 

179.  Name  some  of  the  organized  ferments  found  in  the 
animal  body. 

180.  Name  the  coloring  matters  of  the  tissues  and  fluids 
of  the  animal  body.  To  what  class  of  substances  do  they 
belong  ? 

181.  Name  some  of  the  principal  products  which  are 
found  in  the  animal  body  as  the  result  of  the  decomposi- 
tion and  splitting-up  of  the  albuminous  and  albuminoid 
substances  of  the  body. 

182.  To  what  class  of  substances  do  the  decomposition 
products  of  the  albuminous  and  albuminoid  substances 
belong  ? 

183.  What  is  urea?  Where  is  it  found  in  the  animal 
body? 

184.  How  are  the  organic  nitrogenized  substances  found 
in  the  plants  ? 

185.  What  is  the  ultimate  product  of  the  decomposition 
of  the  albuminous  and  albuminoid  substances  in  the  ani- 
mal body  ? 

6 


LEOTUEE   XI. 

NUTRITION. 

Food. 

The  constant  physiological  activity  of  the  tissues  and 
organs  of  the  animal  body  is  accompanied  by  a  constant 
destruction  and  formation  of  the  substances  composing  the 
tissues  and  organs  of  the  body.  This  constant  formation 
and  destruction  of  substances  in  the  animal  body  is  called 
the  metabolism  of  the  tissues.  It  consists  of  two  distinct 
phases — namely,  (a)  the  destructive  metabolism,  katabol- 
ism,  or  dissimilation,  and  (6)  the  constructive  metabolism, 
anabolism,  or  assimilation.  The  metabolic  processes 'con- 
sist of  a  series  of  chemical  changes,  and  result  in  the  pro- 
duction of  the  forces,  motion  and  heat.  The  katabolic 
changes  result  in  the  production  of  substances  which,  as 
effete  products,  are  eliminated  from  the  body  with  the 
excretions. 

The  anabolic  changes  necessitate  the  introduction  of 
materials  from  which  the  tissue  substances  are  formed. 
These  nutritive  materials  are  introduced  into  the  body  with 
the  food. 

The  nutritive  materials  required  by  the  animal  body  may 
be  enumerated  as  follows:  inorganic  substances — viz., 
water  and  salts;  organic  substances — viz.,  carbohydrates, 
fats,  and  albuminous  substances. 

The  food,  in  order  to  maintain  the  nutritive  functions  in 
the  body,  must  contain  all  these  substances  in  proper  quan- 
tity and  quality,  and  the  organism  suffers  seriously  if  de- 
prived, for  any  length  of  time,  of  one  or  the  other  nutritive 
materials  mentioned. 


FOOD.  83 

Herhivora  are  those  animals  which  derive  their  organic 
food  from  vegetables  and  plants  only,  and  their  organism 
is  capable  of  transforming  the  organic  material  so  obtained 
into  material  for  its  own  tissue.  Carnivora  are  those 
which  derive  their  organic  food  from  the  animal  kingdom 
only.  Omnivora — to  which  man  belongs — take  their  or- 
ganic food  from  the  animal  and  vegetable  kingdoms. 

We  select  for  our  food  articles  which  contain  the  mate- 
rials required  for  the  nutrition  of  our  organism. 

1.  Inorganic  substances,  ivater  and  salts.  These  are 
partly  taken  as  such,  partly  with  other  articles  of  food  of 
which  they  are  ingredients. 

2.  Organic  substances,  (a)  Vegetable — cereals,  such  as 
wheat,  rye,  oats,  barley,  rice,  etc. ;  leguminous  fruits,  such 
as  peas,  beans,  lentils,  etc. ;  potatoes,  vegetables  and  salads, 
fruits  ;  stimulants — coffee  and  tea,  alcoholic  stimulants, 
spices.     (6)  Animal — meats,  milk,  eggs. 

Food  in  order  to  be  nutritious  must  be  pure;  it  must  con- 
tain in  proper  quantity  and  quality  all  the  materials  re- 
quired by  the  organism;  it  must  be  properly  prepared  and 
palatable,  and  it  must  be  adapted  to  the  climate,  to  the 
work  the  individual  performs,  and  to  the  age  of  the  iu  di- 
vidual. 

In  the  following  I  will  describe  briefly  the  articles  chosen 
by  man  for  food  : 

Water  constitutes  about  58.5.  per  cent  of  the  whole  body, 
and  the  great  importance  of  a  constant  exchange  is  clear 
when  we  take  into  consideration  the  many  important  uses 
of  water  in  the  body.  The  average  quantity  of  water  re- 
quired by  the  healthy  adult  is  2,500  to  2,800  cubic  cen- 
timetres in  twenty-four  hours.  Rain-water  and  that  of 
wells,  springs,  rivers,  and  streams  is  used  for  drinking 
purposes.  Rain-water  which  is  collected  in  reservoirs  and 
in  cisterns  is  the  purest.  The  water  of  wells,  and  espe- 
cially that  of  springs,  generally  contains  various  mineral 
ingredients,  a  small  quantity  of  oxygen,  and  a  larger  quan- 


84       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

tity  of  carbon  dioxide.  Tlie  water  of  running  waters — 
rivers,  streams,  etc. — is  the  most  impure,  and  requires 
purification  by  filtration,  etc.,  before  it  can  be  used  for 
drinking  purposes. 

Good  drinking-water  must  hepui^e,  clear,  colorless,  odor- 
less, and  tasteless. 

The  more  common  impurities  of  water  are  : 

(a)  The  salts  of  calcium  and  magnesium  with  CO^. 

(6)  Sulphuric  acid  and  sulphates. 

(c)  Chlorine  and  chlorides. 

{d)  Nitrates  and  nitrites. 

(e)  Sulphuretted  hydrogen. 

(/)  Ammoniates. 

ig)  Organic  ingredients  and  bacteria. 

The  salts  of  calcium  and  magnesium  with  CO^  render 
water  hard,  and,  when  too  abundant,  make  it  unfit  for 
drinking.  The  relative  hardness  of  water  is  determined  by 
the  time  required  to  produce  foam  when  soap  is  shaken 
with  the  water  ;  it  generally  takes  longer  with  hard  water. 
The  hardness  of  drinking  water  must  not  exceed  twenty 
degrees  ;  one  degree  of  hardness  means  1  part  of  the  salts 
of  calcium  and  magnesium  with  COo  to  100,000  parts  of 
water.  The  hardness  of  water  can  be  reduced  to  some  ex- 
tent by  boiling.  The  various  other  inorganic  impurities 
can  often  be  recognized  by  the  taste  and  odor  when  they 
are  contained  in  the  water  to  such  an  extent  as  to  make  it 
unfit  for  drinking  purposes. 

One  of  the  greatest  qualifications  of  good  drinking-water 
is  that  it  does  not  contain  any  organic  ingredients.  Stag- 
nant waters,  and  waters  in  the  vicinity  of  privies,  stables, 
dunghills,  cemeteries,  etc.,  are  often  contaminated  by 
organic  impurities.  Their  presence  is  determined  by  the 
presence  of  nitrogen  or  nitric  acid;  and  also  by  the  recog- 
nition, under  the  microscope,  of  many  micro-organisms 
which  develop  in  such  water.  It  has  been  found  that 
diseases  such  as  typhoid  fever,  dysentery,  malarial  fever. 


FOOD.  85 

etc.,  are  caused  by  drinking  impure  water  contaminated 
with  organic  impurities  ;  and  for  this  reason,  in  locaHties 
where  contamination  with  organic  impurities  is  possible, 
the  water  should  be  well  boiled  before  use. 

The  inorganic  salts  which  constitute  a  part  of  our  or- 
ganism are  taken  in  as  such  with  the  various  articles  of 
food.  When  the  system  is  deprived  of  these  there  results 
an  insufficient  nutrition  of  the  tissues  of  which  they  con- 
stitute a  part. 

2.  The  organic  food  substances:  (a)  The  cereal  fruits — 
wheat,  rye,  corn,  and  rice— are  the  most  important  of  the 
vegetable  kingdom. 

According  to  J.  Koenig,  the  chemical  composition  of 
these  cereals  is  as  follows : 

Albumen 
Water,      material.      Starch.       Sugar.     Dextrin.       Fat.     Cellulose.     Ash. 

Wheat...  .13.56        12.43        64.07  1.44        3.38        1.70        3.66        1.79 

Rye 15.36        11.43        63.00  0.95        4.88        1.71        2.00        1.77 

Corn 13.88        10.05        58.96  4.59        3.33        4  76        2.84        1.69 

Rice 14.41  6.94  77^61  0.51        0.08        0.45 

From  this  table  it  will  be  seen  that  these  cereal  fruits 
contain:  1,  water;  2,  albuminous  material;  3,  starch; 
4,  sugar;  5,  dextrin;  6,  fat;  7,  cellulose;  8,  salts.  The 
latter  are  principally  the  salts  of  magnesium,  calcium, 
and  phosphorus;  chlorides  and  salts  of  sodium  are  but 
sparingly  present,  and  it  is  therefore  necessary  that  such 
salts — i.e.,  sodium  chloride — be  added  in  the  preparation  of 
these  cereals.  The  grains  of  the  cereals  are  ground  to 
flour,  and  this  is  principally  used  in  the  preparation  of 
bread.  The  table  also  shows  that  wheat  contains  the 
greatest  percentage  of  albuminous  matter  in  these  cereals, 
and  it  is  therefore  the  most  nutritious.  Barley,  oats,  etc., 
are  not  easily  digested,  on  account  of  the  great  quantity 
of  cellulose  they  contain. 

The  leguminous  fruits  used  as  food  articles  are:  beans, 
peas,  lentils,  etc.  They  contain  from  22  to  24  per  cent  of 
albuminous  material,  50  to  54:  per  cent  of  carbohydrates,  and 


86      LECTURES    ON    HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

4  to  8  per  cent  of  cellulose.  On  account  of  the  large  percent- 
age of  the  albuminous  material  legumin,  they  are  valuable 
and  nutritious  foods. 

Potatoes  contain  76  per  cent  of  water,  20  per  cent  of 
starch,  about  1.70  per  cent  of  albuminous  material,  and 
0.97  per  cent  of  inorganic  salts. 

Vegetables  are  the  roots  and  leaves  of  many  plants,  and 
contain  starchy  material,  sugar,  inorganic  salts,  and  or- 
ganic acids.  The  salts  and  organic  acids  render  these 
valuable  articles  of  food. 

Fruits  contain  sugar,  dextrose,  starch,  and  acids  such 
as  citric,  tartaric,  acetic,  and  oxalic;  the  latter  principally 
stimulates  the  appetite. 

Stimulants,  (a)  Alcoholic  stimulants,  such  as  wines, 
beers,  whiskeys,  brandies;  (6)  coffee,  tea,  cocoa,  and  choco- 
late; (c)  spices.  These  substances  are  principally  taken  to 
stimulate  the  secretion  of  the  digestive  juices. 

[b)  Tlie  animal  food  articles.  Meat  constitutes  the 
principal  article  of  animal  food.  It  contains  myosin  of 
the  muscle-tissues,  serum-albumin  of  the  juice,  gelatin  of 
the  connective  tissues,  elastiu  of  the  elastic  tissues,  and, 
besides  these,  haemoglobin,  fatty  matter,  salts,  and  water. 

The  meats  generally  used  are  the  flesh  of  the  ox — beef 
and  veal;  that  of  the  sheep — lamb  and  mutton;  and  that 
of  the  pig — pork,  bacon,  and  ham.  Of  these  beef  contains 
the  largest  amount  of  albuminous  matter — about  20  per 
cent — and  is  therefore  the  most  nutritious.  Veal  and  lamb 
are  less  digestible  than  the  other  meats.  Pork  contains 
only  about  10  per  cent  of  albuminous  matter,  but  about  48 
per  cent  of  fat;  it  is  therefore  not  easily  digested  and  least 
nutritious.  Poultry,  venison,  and  fish,  and  many  animals 
living  in  water,  such  as  oysters,  lobsters,  etc.,  must  also  be 
considered  as  meats.  Poultry  is  very  nutritious;  it  con- 
tains about  21  per  cent  of  albuminous  matter. 

Letheby  gives  the  composition  of  the  food  articles  of 
this  class  as  follows: 


V  FOOD.  87 

Water.  Albumen.  Fats.  Salts- 
Beef 72  19.3  3.6  5.1 

Teal 63  16.5  15.8  4.7 

Mutton 72  18.3  4.9  4.8 

Pork 39  9.8  48.9  2  3 

Poultry 74  210  3.8  1.2 

Whitefish 78  18.1  2.9  1.0 

Oysters 75  11.72  2.42  2.73 

The  percentages  given  are  those  of  lean  meat.  These 
meats  when  fat  contain  a  greater  proportion  of  fat  and  a 
smaller  proportion  of  water  and  albuminous  material. 

The  meats  are  prepared  for  eating  by  cooking;  this  pro- 
duces certain  changes  in  the  meats  which  increase  their 
digestibility. 

The  boiling  of  meat  causes  the  extraction  of  the  soluble  al- 
buminous materials,  the  fats,  salts,  etc.,  which,  dissolved 
in  the  water,  constitute  the  meat-extract.  The  albuminous 
matters  coagulate  and  form  a  grayish  foam,  which  floats 
on  the  surface  of  the  water.  The  meat-extract  or  broth 
thus  prepared  contains,  therefore,  no  albuminous  matter. 
The  meat  so  boiled  contains  the  myosin,  which  is  coagu- 
lated, and  it  is  for  this  reason  not  very  digestible.  Together 
with  fat,  salts,  and  spices  it  is  still  a  nutritious  food. 

Fried  meats  are  more  digestible  and  have  a  greater 
nutritive  value  than  boiled.  The  reason  for  this  is  that 
during  the  process  of  frying  the  albuminous  materials  on 
the  surface  are  only  firmly  coagulated,  and  the  other  mate- 
rials are  not  extracted  to  such  a  degree. 

Meat-extracts  are  prepared  by  extracting  the  soluble 
materials  of  meat  with  cold  water;  from  the  extract  so 
obtained  the  gelatin,  albumen,  and  fat  are  removed. 

Other  methods  of  preparing  meats  are  smoking,  pick- 
ling, drying,  and  canning;  these  serve  to  preserve  the  meat. 

Raw  meat  is  not  easily  digested;  it  must,  therefore,  be 
scraped  very  fine  if  it  is  to  be  eaten  in  a  raw  condition. 
The  meat  of  the  pig  should  never  be  eaten  raw,  on  account 
of  the  occasional  appearance  of  the  trichina  spiralis  and 


88       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

of  the  organism  from  which  the  tapeworm  {tcenia  solium} 
develops.  Great  care  should  be  taken  to  avoid  eating 
meats  in  a  state  of  decomposition,  as  in  them  are  often 
found  substances  which  are  deleterious  to  the  health. 

Milk  is  the  secretion  of  the  mammary  glands  of  the  fe- 
male. The  mammary  glands  are  compound  acinous  glands \ 
their  cells  possess  the  property  of  transforming  blood  con- 
stituents into  those  of  the  milk. 

Milk  is  composed  of  water,  casein,  albumen,  fat,  sugar, 
and  salts,  principally  chlorides  and  phosphates.  This  com- 
position of  the  milk  makes  it  a  valuable  food  article. 
Cow's  milk  is  generally  used  by  adults;  also  the  milk  of 
goats  and  asses.  To  the  feeding  of  infants  mother's  milk 
is  best  adapted,  because  it  is  rich  in  milk-sugar  and  con- 
tains more  albumen  than  casein,  which  causes  it  to  co- 
agulate in  the  infant's  stomach  in  fine  flocks.  Ass's  milk, 
in  its  composition,  resembles  mother's  milk,  and  is  for  this- 
reason  often  used  as  a  substitute.  Cow's  milk  contains 
more  casein  than  albumen;  it  consequently  coagulates  in 
the  stomach  in  large,  hard,  indigestible  masses.  It  also 
contains  a  smaller  percentage  of  sugar  than  mother's  milk, 
and  for  these  reasons  must  be  diluted  and  an  addition  of 
sugar  made  in  order  to  be  serviceable  as  a  substitute  for 
mother's  milk.  Goat's  milk  contains  a  still  larger  quantity 
of  casein  than  cow's  milk.  The  main  objection  to  the  use 
of  animal  milk  as  a  substitute  for  mother's  milk  in  the 
feeding  of  infants  is  the  fact  that  in  the  former  micro- 
organisms are  often  developed  which  are  deleterious  to  the 
health  of  the  infant  and  which  make  it  necessary  to  ster- 
ilize or  pasteurize  it  before  use. 

Butter  and  cheese  are  made  from  milk.  Another  prepa- 
ration of  milk  is  an  alcoholic  drink  called  kumyss.  It  is 
made  by  the  fermentation  of  the  milk-sugar,  which  pro- 
duces alcohol. 

J.  Koenig  gives  the  following  quantitative  composition 
of  milk: 


FOOD.  89- 


Water. 

Casein. 

Albumen. 

Fat. 

Sugar. 

Salts. 

Mother's 

milk . . . . 

87.09 

0.63 

1.31 

3.90 

6.04 

0.49 

Cow's 

ii 

87.41 

3.01 

0.75 

3.66 

4.82 

0.70 

Goat's 

(( 

85.91 

2.87 

1.19 

4.09 

4.45 

0.66 

Ass's 

(( 

90.04 

0.60 

1.55 

1.39 

6.25 

0.31 

Milk  is  a  slightly  alkalioe,  white  fluid.  It  does  not  co- 
agulate when  heated.  On  standing  it  sours,  due  to  the 
decomposition  of  the  milk-sugar  and  the  production  of 
lactic  acid.  This  is  due  to  the  bacterium  lactis,  the  germs 
of  which  are  contained  in  the  air.  In  sour  milk  the  casein 
is  coagulated. 

Eggs,  principally  those  of  birds,  are  very  valuable  as 
food.  They  contain  in  proper  proportions  all  materials 
essential  for  the  nutrition  of  the  body. 

An  egg  is  composed  of  a  white  and  a  yolk.  The  white 
of  egg  contains  water  85  per  cent,  albuminous  matter  12^ 
percent,  fat  0.25  per  cent,  and  salts  0.59  per  cent,  prin- 
cipally chlorides  of  sodium  and  potassium.  The  yolk  of 
the  egg  contains  water  50.8  per  cent,  albuminous  material 
16.25  per  cent,  fat  31.75  per  cent,  and  salts  1  per  cent,  prin- 
cipally salts  of  phosphorus  and  lime.  Of  the  two  the  yolk 
contains  the  more  nutritious  material  and.  is  more  easily 
digested.  Eggs  when  soft-boiled  are  most  digestible,  be- 
cause the  albuminous  material  of  the  egg  is  coagulated  in 
fine  flocks. 

From  this  description  of  the  various  food  articles  we 
learn  that  most  of  them  contain  in  proper  proportions  the 
essential  ingredients  of  food — namely,  water,  inorganic 
salts,  albuminous  material,  carbohydrates,  and  fats. 

The  absolute  quantity  of  these  essential  food  constituents 
which  an  individual  requires  depends  upon  the  age,  sex, 
occupation,  and  climatic  conditions. 

It  may  be  said  that,  in  order  to  maintain  the  equilibrium 
of  nutrition  in  the  body,  the  elementary  composition  of  the 
nutritive  material  taken  must  be  equal  to  the  elementarj^ 
composition  of  the  effete  products  eliminated  from  the 
body. 


90       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

When  the  elaboration  of  more  heat  in  the  body  is  re- 
quired, as  is  the  case  in  cold  weather,  and  when  great 
muscular  work  is  done  by  the  individual,  then  the  dissimi- 
lation of  the  tissue  substances  is  increased  and  necessitates, 
the  taking  of  more  nutritious  material. 

During  the  growth  and  development  of  the  individual 
the  nutritious  material  taken  should  be  greater  than  the 
effete  material.  In  old  age  the  materials  excreted  gene- 
rally exceed  in  their  elementary  composition  that  of  the 
nutritive  materials  taken. 

The  want  of  nutritive  material  is  indicated  by  hunger 
and  thirst.  An  insufficient  supply  of  nutritive  materials 
is  indicated  by  loss  of  weight.  The  loss  which  the  tissues 
suffer  during  the  inanition  varies  in  the  different  organs. 
Adipose  tissue  and  muscles  lose  first  and  most.  Starvation 
is  indicated  by  loss  of  weight  and  decrease  of  nitrogenous 
effete  products. 

In  man  death  from  starvation  occurs  in  about  three 
weeks  ;  in  the  last  stages  there  is  a  general  debility,  de- 
creased temperature,  and  coma. 

The  average  quantity  of  the  various  food  materials  daily 
required  by  an  adult  has  been  estimated  to  be:  water,  2,500 
to  2,800  grammes  ;  inorganic  salts,  32  grammes  ;  albu- 
minous substances,  130  grammes ;  fats,  84  grammes  ;  car- 
bohydrate material,  400  grammes  ;  oxygen  (inhaled  with 
the  air),  744  grammes. 

From  this  table  it  may  be  seen  that  food  should  contain 
organic  nitrogenized  and  organic  non-nitrogenized  mate- 
rials in  a  proportion  of  1  to  4  or  1^  to  4^. 

The  inorganic  food  materials  are  taken  in  as  such  with 
the  food  and  drink,  and  they  are  eliminated  as  such  with 
the  excreta. 

The  organic  food  materials  are  composed  of  the  follow- 
ing elementary  constituents  :  carbon,  nitrogen,  hydrogen, 
oxygen,  phosphorus,  sulphur,  and  iron.  These  materials 
are  assimilated  into  tissue  substances  and  undergo  changes; 


FOOD.  91 

they  are  'finally  excreted  as  urea,  carbon  dioxide,  and 
water,  which  contain  the  same  elementary  substances. 

The  nutritive  values  of  the  various  food  materials  differ. 

The  albuminous  substances  must  be  considered  as  the 
most  important.  The  animal  cell  is  capable  of  reproduc- 
ing its  own  living  material  from  albuminous  material  only, 
for  which  no  other  nitrogenized  substance,  such  as  albu- 
minoid, gelatin  or  gluten,  etc.,  can  be  substituted.  If  the 
cell  is  deprived  of  a  supply  of  albuminous  material  it  dies. 

Albuminous  materials  contain  all  the  elements  required 
for  the  tissue -formation  in  the  body.  Experiments  have 
been  made  to  determine  whether  animals  cannot  be  sus- 
ta,ined  by  feeding  them  with  albuminous  material  and 
inorganic  foods  alone.  It  has  been  demonstrated  that  for 
a  short  time  this  can  be  done,  because  albuminous  material 
is  transformed  in  the  body  into  the  living  matter  of  the 
cells  and  also  into  carbohydrates  and  fat.  The  experi- 
ments could  not  be  continued  for  a  long  time,  because  the 
animals  required  such  enormous  quantities  of  albuminous 
material  in  order  to  renew  the  quantity  of  carbon  and 
hydrogen  which  is  constantly  eliminated  from  the  body 
with  the  carbon  dioxide  and  water.  The  quantities  of 
albuminous  materials  required  to  do  this  are  so  great  that 
the  animal  organism  is  incapable  of  elaborating  them. 

Carbohydrates  and  fat  cannot  alone  support  life,  because 
they  do  not  contain  nitrogen.  They  are  principally  calori- 
facious  foods,  owing  to  the  rapid  combustion  of  the  car- 
bon and  hydrogen  they  contain. 

The  nutritive  value  of  the  inorganic  ingredients  of  the 
food  is  explained  by  their  many  uses  and  wide  distribu- 
tion as  tissue  constituents. 

Before  finishing  this  subject  I  will  describe  the  effects  of 
over-feeding. 

I  have  before  stated  that  albuminous  material  contains 
all  the  necessary  elementary  constituents  of  life,  whereas 
fat  and  carbohydrates  alone  cannot  support  life.    The  ani- 


92       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

mal  digestive  apparatus  is  capable  of  digesting  a  greater 
quantity  of  food  than  is  required  to  maintain  an  equili- 
brium of  nutrition. 

An  over-feeding  with  albuminous  materials  generally 
results  in  an  increased  excretion  of  the  products  of  the 
dissimilative  process  of  the  tissues.  Only  a  small  quantity 
of  the  plus  of  albuminous  material  is  transformed  into 
tissue-substance,  resulting  in  an  increase  of  flesh. 

An  over-feeding  with  fat  and  carbohydrate  material 
results  in  an  increase  of  fat-tissue,  if  the  quantity  of  albu- 
minous material  given  with  the  fat  and  carbohydrate  food 
is  that  quantity  which  would  be  required  to  maintain  the 
nutritive  equilibrium  without  the  addition  of  any  fat  or 
carbohydrate  material. 

The  result  of  an  excessive  tissue-formation  is  obesity; 
this  is  not  necessarily  an  increase  of  fat-tissue  only,  but 
often  an  increase  of  flesh.  The  condition  is  generally  the 
result  of  an  excessive  taking  of  nutritive  materials,  but 
often  it  is  also  due  to  an  abnormal  condition  of  the  meta- 
bolic processes  in  the  body,  as  is  the  case,  for  instance,  in 
hereditary  obesity. 

The  conditions  favoring  obesity  are  as  follows:  a)  Tak- 
ing of  large  quantities  of  albuminous  substances  and  fat  or 
carbohydrate  material.  If  the  quantity  of  albuminous 
material  is  decreased,  an  increase  of  fat  or  carbohydrate 
material  is  necessary;  in  such  a  case  no  increased  forma- 
tion of  fat  will  take  place  in  the  body.  Carbohydrate 
material  is  transformed  to  a  certain  extent  into  fat. 

(6)  A  decrease  of  the  katabolic  processes  in  the  body,  as 
takes  place  when  the  muscular  and  mental  activity  is 
decreased. 

(c)  Conditions  decreasing  the  red  blood-corpuscles,  they 
being  the  oxygen-carriers,  result  in  the  decrease  in  the  sup- 
ply of  oxygen  and  in  the  j^rocesses  of  oxidation  in  the  body. 

{d)  The  imbibing  of  alcohol,  which,  being  rapidly  oxi- 
dized in  the  body,  prevents  a  rapid  oxidation  of  fat. 


QUESTIONS   AND   EXERCISES.  93 

(e)  Phlegmatic  temperament,  small  mental  activity,  also 
favor  an  excessive  development  of  flesh  and  fat,  whereas 
excitement,  great  mental  work,  strain,  worry,  etc.,  are 
conditions  opposing  obesity. 

People  suffering  from  obesity  should  observe  the  follow- 
ing rules: 

(a)  The  gradual  reduction  of  all  nutritious  material. 

(b)  The  increase  of  muscular  activity. 

(c)  Increase  in  the  elimination  of  heat  from  the  body  by 
cool  baths. 

(d)  The  increase  and  stimulation  of  the  circulation  by 
friction  and  massage.  Care  should  be  taken  to  avoid  a 
partial  reduction  or  a  total  abstinence  from  any  one  class 
of  nutritious  materials.  The  amount  of  fat  and  carbo- 
hydrate foods  should  be  reduced  first.  This  necessitates 
a  slight  increase  of  albuminous  foods. 

In  dieting  for  obesity  no  liquids  should  be  taken  with  the 
food,  as  they  retard  absorption  and  digestion. 

Another  frequent  result  of  over-feeding  is  indigestion, 
caused  by  a  decomposition  of  food  in  the  alimentary  canal, 
resulting  in  the  formation  of  the  products  of  putrefaction. 

Gout  is  considered  the  result  of  over-feeding  with  albu- 
minous materials;  they  are  mainly  elaborated  in  the  liver, 
but  as  this  organ  is  unable  to  elaborate  a  great  excess  of 
albuminous  material,  the  incomplete  oxidation  of  the  mate- 
rials causes  the  pathological  condition  known  as  gout. 

The  quantity  and  quality  of  food  materials  required  at 
the  different  ages  depend  upon  the  condition  of  the  diges- 
tive organs  and  juices,  and  I  will  speak  of  this  more  in 
detail  in  a  later  lecture. 


QUESTIONS   AND   EXERCISES. 

Subject. — Food. 
Lecture  XI. 

186.  What  do  you  understand  by  metabolism,  anabolism, 
katabolism,  assimilation,  dissimilation  ? 


94      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY'. 

187.  What  are  the  effects  of  the  metabolism  of  the  tis- 
sues? 

188.  What  is  meant  by  food  ? 

189.  Name  the  essential  nutritive  materials. 

190.  What  do  you  understand  by  herbivora,  carnivora, 
omnivora  ? 

191.  What  is  the  quantity  of  water  required  by  an  adult 
in  twenty-four  hours  ? 

192.  What  uses  does  water  serve  in  the  animal  organism? 

193.  What  are  the  sources  of  drinking-water  ? 

194.  Name  some  impurities  of  water. 

195.  What  should  be  the  properties  of  good  drinking- 
water  ? 

196.  What  produces  hardness  of  water  ? 

197.  What  is  meant  by  a  degree  of  hardness  ? 

198.  What  maximum  degree  of  hardness  may  potable 
water  have  ? 

199.  What  effect  has  boiling  on  water  ? 

200.  Name  some  vegetable  articles  chosen  by  man  as 
food. 

201.  Which  of  the  cereals  has  the  greatest  amount  of 
albuminous  substance  ? 

202.  Name  the  principal  leguminous  fruits  chosen  by 
man  as  food. 

203.  Give  the  composition  of  potatoes. 

204.  Explain  the    nutritive  value    of    the    stimulating 
foods. 

205.  Name  the  principal  meats  used  as  food. 

206.  Which  of  the  meats  has  the  most  nutritive  value  ? 

207.  Why  should  not  meats  be  eaten  in  a  raw  condition  ? 

208.  What  is  the  effect  of  boiling  or  frying  meats  ? 

209.  Why  is  fried  meat  more  nutritious  and  more  easily 
digested  than  boiled  meat  ? 

210.  Which  of  the  meats  contain  the  greatest  percentage 
of  albuminous  material  ? 

211.  Where  is  milk  formed  ? 


QUESTIONS  AND    EXERCISES.  95 

212.  Give  the  composition  of  cow's  milk,  mother's  milk, 
goat's  milk,  and  ass's  milk  ? 

213.  Why  is  mother's  milk  most  preferable  for  feeding 
infants  ? 

o  214.  How  should  cow's  milk  be  prepared  in  order  to  serve 
as  a  substitute  for  mother's  milk  ? 

215.  Give  food  articles  prepared  from  milk. 

216.  Give  the  composition  of  the  white  and  the  yolk  of 
the  egg. 

217.  Name  the  elements  contained  in  the  various  nutri- 
tious articles. 

-  218.  What  is  the  quantity  of  albuminous  material  re- 
quired by  an  average  adult  in  twenty-four  hours  ? 

219.  Can  any  other  nitrogenous  materials  be  substituted 
for  the  albuminous  substances  ?    Explain  in  detail. 

220.  What  is  the  quantity  of  fat  and  of  carbohydrate  ma- 
terial required  by  an  average  adult  in  twenty-four  hours  ? 

221.  Can  the  life  of  an  animal  be  sustained  when  it  is 
fed  only  with  non-nitrogenous  organic  materials  ?   Explain. 

222.  What  is  the  quantity  of  inorganic  salts  required  by 
an  average  adult  in  twenty-four  hours  ? 

223.  What  is  meant  by  the  equilibrium  of  nutrition  ? 

224.  What  conditions  make  an  increase  in  the  supply  of 
nutritive  materials  necessary,  and  why  ? 

225.  What  would  be  the  result  of  an  insufficient  supply 
of  nutritive  materials  ? 

226.  Which  structures  of  the  body  suffer  most  as  a  result 
of  starvation  ? 

227.  What  should  be  the  relation  of  the  albuminous 
material  and  the  organic  non-nitrogenous  materials  (fat, 
starches,  sugars)  in  a  mixed  diet  ? 

228.  In  what  form  are  the  elementary  constituents  of 
the  organic  nutritious  materials  taken  in  and  eliminated 
from  the  body  ? 

229.  Compare  the  nutritive  value  of  albuminous  sub- 
stances with  that  of  fats  and  carbohydrates. 


^6       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

230.  Name  the  qualities  which  food  should  have  in  order 
to  be  good  and  nutritious. 

231.  Name  three  kinds  of  food  from  which  starch  is  de- 
rived, and  give  the  percentage  of  starch  in  each. 

232.  Name  diseases  produced  by  drinking  impure  w^ater. 

233.  Show  the  value  of  eggs  as  an  article  of  food. 

234.  Name  some  of  the  impurities  found  in  rain-water 
that  is  stored  in  cisterns. 

235.  Name  four  inorganic  substances  that  should  be  pre- 
sent in  our  food,  and 

236.  State  why  each  is  important. 

237.  What  danger  often  exists  in  water  used  for  drink- 
ing, and  how  can  such  danger  be  averted  ? 

238.  Are  inorganic  ingredients  of  food  necessary  to  sus- 
tain life  ?    Why? 

239.  Are  albuminous  matters  solid  or  fluid  ?    Where  are 
they  found  in  the  body  ? 

240.  What  advantage  is  derived  from  a  mixed  diet  ? 

241.  Mention  the  non-nitrogenous  constituents  of  food 
and  the  nutritive  value  of  each. 

242.  Name  eight  principal  carbohydrates  used  for  food. 

243.  What  effect  does  an  excessive  starch  diet  produce  ? 

244.  What  is  the  composition  of  human  milk  ? 

245.  What  kind  of  foods  would  you  recommend  in  cases 
of  obesity  ? 

246.  What   are    amyloid     foods  ?    Albuminous    foods  ? 
•Give  three  examples  of  each. 

247.  Describe  the  physiological  causes  of  obesity. 

248.  Discuss  the  effect  of  cooking  food  as  a  means  of 
rendering  it  more  digestible. 

249.  What  is  the  daily  quantity  of  food  required  to  nour- 
ish the  human  system  ? 

250.  Mention  the  essential  elements  of  foods.     Give  the 
relative  food-value  and  ease  of  digestion  of  the  meats. 

251.  What  diet  should  be  prescribed  to  reduce  obesity  ? 


LEOTUEE  XII. 

DIGESTION. 

By  the  word  digestion  we  mean  a  series  of  chemical  and 
physical  processes  by  which  the  articles  of  food,  while  in 
the  alimentary  canal,  are  rendered  absorbable. 

The  chemical  processes  of  digestion  include  the  action  of 
the  various  digestive  juices  upon  the  foods.  The  physical 
or  mechanical  processes  include  the  chewing  and  swallow- 
ing of  the  food  and  the  peristaltic  movements  of  the  stom- 
ach and  intestines,  which  have  for  their  purpose  the  thor- 
ough mixing  of  the  food  with  the  digestive  juices  and  the 
conveying  of  it  onward  in  the  alimentary  canal. 

The  digestive  apparatus  consists  of  the  alimentary  canal 
and  a  number  of  accessory  organs — viz.,  the  salivary 
glands,  the  liver,  and  the  pancreas. 

The  alimentary  canal  begins  at  the  mouth  and  ends  at 
the  anus.  It  is  lined  throughout  its  whole  length  with 
raucous  membrane,  and  has  opening  into  it  the  numerous 
glands  which  secrete  the  digestive  juices. 

The  alimentary  canal  is  divided  into  various  portions, 
which,  in  their  order,  are  as  follows:  mouth,  buccal  cavity, 
pharynx,  oesophagus,  stomach,  small  intestines,  and  large 
intestines. 

In  man  the  alimentary  canal  is  about  six  times  the 
length  of  the  whole  body. 

The  digestive  juices  are  the  saliva,  gastric  juice,  pan- 
creatic juice,  intestinal  juice,  and  bile. 

The  process  of  digestion  consists  of  seven  stages — viz.  : 

1.  Prehension. 

2.  Mastication. 

7 


98      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY, 

3.  Insalivation. 

4.  Deglutition.  ^ 

5.  Stomach  digestion. 

6.  Intestinal  digestion. 

7.  Defecation. 

I  will  describe  the  several  stages,  together  with  the  ana- 
tomy and  structure  of  the  various  portions  of  the  digestive 
apparatus,  and  the  composition,  action,  and  mode  of  secre- 
tion of  the  various  digestive  juices. 

1.  Prehension. 

The  act  by  which  the  food  is  introduced  into  the  buccal 
cavity  is  called  prehension.  Man  uses  his  hands  and  lips 
for  this  purpose. 

The  buccal  cavity  is  the  upper  portion  of  the  alimentary 
canal,  into  which  the  food  is  introduced  through  the  ante- 
rior orifice,  the  mouth.  The  buccal  cavity  is  oblong  and 
arched.  Its  boundaries  are  as  follows  :  In  front,  the  lips, 
the  alveolar  processes  of  the  jaws,  and  the  teeth  contained 
therein  ;  behind,  it  is  continuous  with  the  pharynx  through, 
the  fauces  ;  laterally  it  is  enclosed  by  the  cheeks,  by  the 
alveolar  processes  of  the  jaws,  and  by  the  teeth  ;  the  roof 
is  arched,  and  is  formed  by  the  hard  palate  in  front  and 
the  soft  palate  behind.  The  floor  is  formed  of  soft  parts, 
which,  from  within  outward,  may  be  enumerated  as  fol- 
lows :  mucous  membrane,  subnmcous  tissue,  supporting- 
glands  and  vessels,  muscles — viz.,  the  mylo-hyoid  and  the 
genio  hyoid — subcutaneous  tissue,  and  skin.  The  tongue 
also  forms  part  of  the  floor  of  the  buccal  cavity. 

Opening  into  the  cavity  are  numerous  glands — viz.,  the 
salivary  glands  and  the  mucous  follicles.  The  whole  buccal 
cavity  is  lined  with  mucous  membrane,  which  is  covered 
with  flat,  stratified  epithelium.  In  the  mouth  the  food  is- 
masticated  and  insalivated. 

2,  Mastication. 

The  act  of  chewing  or  masticating  has  for  its  purpose 
the  division  of  the  solid  parts  of  food  into  small  particles, 


MASTICATION.  99 

SO  that  these  may  be  more  easily  permeated  and  attacked 
by  the  digestive  juices.  From  this  it  is  clear  that  a  proper 
mastication  of  the  food  is  essential  for  its  digestion,  and 
a  proper  mastication  is  possible  only  when  the  principal 
organs  of  mastication — i.e.,  the  teeth — are  in  proper  order. 
The  teeth  in  the  various  classes  of  animals  are  shaped  and 
arranged  in  a  manner  most  suitable  for  the  mastication  of 
the- food  taken  by  them.  The  herbivora  have  teeth  with 
large,  flat,  corrugated  grinding  surfaces.  The  carnivora 
have  teeth  with  cutting  edges  ;  these  have  points  or  cusps 
for  the  tearing  of  flesh.  The  omnivora,  to  which  man 
belongs,  have  both  the  teeth  of  the  carnivora  and  the 
herbivora. 

The  complete  number  of  teeth  in  the  human  adult  is 
32 — namely,  16  in  each  jaw.  The  8  teeth  contained  in  each 
lateral  half  of  each  jaw  are  called,  beginning  with  the  an- 
terior, 1  central  incisor,  1  lateral  incisor,  1  canine,  2  bicus- 
pids, 2  molars,  and  1  wisdom  tooth. 

Mastication  is  effected  by  an  up-and-down,  and  lateral  or 
grinding,  motion  of  the  lower  jaw,  by  which  the  teeth  are 
brought  against  those  of  the  upper  jaw,  and  the  food, 
which  by  the  motion  of  the  lips,  cheeks,  and  tongue  is 
brought  between  the  teeth,  is  cut,  torn,  and  ground  until 
it  is  well  divided  and  subdivided.  During  mastication  the 
food  becomes  thoroughly  mixed  with  the  saliva  and  forms 
a  soft,  slippery  mass — the  bolus. 

The  movements  of  the  lower  jaw  are  effected  by  the 
muscles  of  mastication,  which  may  be  classified  as  follows: 

{a)  The  muscles  raising  the  lower  jaiu  : 
The  temporal  muscles, 
^         ' '     masseter, 

"    internal  pterygoid. 

(6)  The  muscles  depressing  the  lower  jaw  : 
The  genio-hyoid  muscles, 
' '     mylo-hyoid       ' ' 
"    platysma  myoides, 
"    anterior  portion  of  the  digastric. 


100       LECTURES   ON   HUMAN   PHYSIOLOGY  AND    HISTOLOGY. 

(c)  The  muscles  producing  the  grinding  motion  :  The  ex- 
ternal pterygoid  muscles.  They  bring  the  jaw  forward, 
and  by  their  alternate  contraction  produce  the  lateral  or 
grinding  motion. 

The  act  of  mastication  is  a  voluntary,  but  also  an  invol- 
untary nervous  act. 

The  centre  of  mastication  is  located  in  the  medulla 
oblongata. 

The  sensory  nerves  are  branches  from  the  fifth  and  the 
tenth  cranial  nerves  ;  by  these  the  stimulus — viz.,  the  pre- 
sence of  solid  food  in  the  buccal  cavity — is  conveyed  to  the 
centre. 

The  motor  branches  supplying  the  muscles  of  mastica- 
tion are  from  the  fifth,  seventh,  and  twelfth  cranial  nerves. 
Their  distribution  is  as  follows:  The  muscles  raisiug  the 
lower  jaw  are  supplied  by  branches  from  the  inferior  max- 
illary division  of  the  fifth  cranial  nerve;  the  muscles  de- 
pressing the  lower  jaw — i.e.,  the  mylohyoid  and  anterior 
portion  of  the  digastric — by  branches  from  the  fifth;  the 
genio-hyoid,  by  a  branch  from  the  twelfth;  and  the  pla- 
tysma  myoides,  b)"  a  branch  from  the  seventh  cranial 
nerve. 

The  pterygoid  muscles  receive  motor  branches  from  the 
fifth  cranial  nerve  through  its  inferior  maxillary  division. 

The  Structure  and  Develojwient  of  the  Teeth. — The  teeth 
are  contained  in  the  alveolar  processes  of  the  jaws.  A 
tooth  consists  of  a  crown — viz.,  the  part  projecting  above 
the  gums — and  one  or  more  roots,  which  are  contained  in 
the  alveoli;  the  constricted  portion  between  crown  and 
roots  is  called  the  neck.  The  structures  composing  a  tooth 
are  the  pulp,  the  dentin,  the  enamel,  and  the  cementum. 

The  pulp  is  composed  of  myxomatous  tissue — viz.,  of 
nerve  filaments,  blood-vessels,  and  delicate  fibrillar  tissue 
supporting  these.  The  external  surface  of  the  pulp  is  cov- 
ered with  a  single  layer  of  branched  cells,  resembling  epi- 
thelial cells;  they  are  called  the  odontoblasts.    The  pulp  is 


MASTICATION.  101 

contained  in  the  pulp-chamber,  a  cavity  in  the  interior  of 
the  tooth.  The  structures  composing  the  pulp  enter  by  a 
foramen  at  the  apex  of  each  root,  called  the  apical  fora- 
men, or  foramen  denfium. 

The  dentin  is  developed  from  the  odontoblasts;  it  forms 
the  matrix  or  body  of  the  tooth;  it  consists  of  27.70  per 
cent  of  organic  matter  and  72.30  per  cent  of  inorganic 
matter — viz.,  calcium  and  magnesium  phosphate  and  car- 
bonate, and  traces  of  iron  and  fluorine. 

Examined  under  the  microscope,  dentin  is  seen  to  be^ 
pierced  by  numerous  canaliculi,  which,  in  a  wavy  course, 
radiate  from  the  pulp-chamber  toward  the  periphery;  in 
their  course  these  canaliculi  frequently  anastomose.  The 
dentinal  canaliculi,  as  they  are  called,  are  lined  by  a  deli- 
cate membrane  called  the  dentincd  sheath.  The  canaliculi 
contain  the  delicate  processes  of  the  odontoblasts  covering 
the  pulp;  these  processes  are  called  the  dentinal  fibres ; 
they  terminate  in  the  interglobular  spaces,  which  are  shal- 
low excavations  in  the  outer  surface  of  the  dentin,  between 
this  and  the  enamel. 

The  enamel  is  the  tissue  which  covers  the  crown.  It 
contains  about  3  per  cent  of  organic  and  96  to  97  per  cent 
of  inorganic  matter,  principally  calcium  j)hosphate,  car- 
bonate, and  fluoride,  and  magnesium  phosphate. 

Enamel  consists  of  flattened,  hexagonal  prisms.  They 
are  about  ^m  of  an  inch  thick. 

The  cemeufum,  or  crusta  petrosa,  has  the  structure  of 
bone- tissue.  It  covers  the  roots  of  the  teeth  in  a  thin 
layer.  The  cementum  is  covered  with  a  delicate  vascular 
membrane  called  the  pericementum  or  p)eriodontal  mem- 
brane. This  also  forms  the  periosteum  of  the  alveolus, 
and  is  continuous  with  the  periosteum  covering  the  alve- 
olar process.     ' 

The  crown  of  a  tooth  is  covered  with  a  thin,  structureless 
membrane  called  the  cuticula  or  NasmytlVs  membrane.  It 
is  only  present  a  short  time  and  soon  wears  off. 


102      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  gums  are  the  structures  covering  the  alveolar  pro- 
cesses. They  consist  of  a  mucous  membrane  devoid  of 
mucous  follicles. 

The  development  of  the  teeth  begins  at  about  the  end  of 
the  second  month  of  fcetal  life.  At  about  this  time  there 
develops  upon  the  gum  covering  the  jaws  a  thick,  elevated 
ridge  which  is  composed  of  multiple  layers  of  epithelial 
cells.  At  the  same  time  a  long  depression  or  furrow  de- 
velops in  the  gum  along  the  under  portion  of  the  ridge. 
This  groove  or  furrow  is  called  tlie  dental  groove.  This 
gradually  deepens  into  the  gum-tissue  and  becomes  wi- 
dened in  its  deeper  portion.  The  dental  groove  gradually 
becomes  filled  with  elongated  epithelial  cells,  and  these 
form  in  the  groove  a  mass  which  is  called  the  enamel-or- 
gan. During  the  formation  of  this  a  conical  papilla  is 
developed  from  the  cells  of  the  mucous  membrane  of  the 
gum — namely,  from  the  floor  of  the  dentinal  groove.  The 
papilla,  also  called  the  dentin-gerin,  grows,  and  its  apex  is 
covered  by  the  enamel-organ.  At  about  this  time  the  outer 
cells  of  these  structures  develop  into  connective  tissue, 
which  forms  a  sac  called  the  tooth-sac,  and  enclosed  in  it 
are  the  enamel-organ  and  the  papilla. 

The  enamel-organ  at  this  time  consists  of  layers  of  cells, 
which  are  compressed  by  the  papilla.  The  cells  lying  next 
to  the  papilla  become  calcified  and  develop  into  the  hexa- 
gonal, flat  enamel  prisms,  which  therefore  are  calcified 
epithelial  cells.  Those  cells  of  the  enamel-organ  which  lie 
toward  the  tooth-sac  become  horny  and  form  the  cuticula 
which  in  early  life  covers  the  enamel. 

The  dentin  is  developed  from  the  outer  layers  of  the 
cells  of  the  papilla — viz. ,  the  odontoblasts.  The  remainder 
of  the  papilla  constitutes  the  pulp  of  the  tooth. 

The  cementum  is  developed  from  the  lower  portion  of 
the  dentinal  sac  by  a  process  of  ossification. 

The  human  being  is  provided  with  two  sets  of  teeth, 
called  respectively  the  temporary  and  the  permanent. 


MASTICATION.  103 

The  temporarij  set  consists  of  20  teeth,  10  in  each  jaw. 
They  are  enumerated  from  the  front  as  follows:  2  central 
incisors,  2  lateral  incisors,  2  canines,  2  first  molars,  2  sec- 
ond molars.  The  formation  of  the  teinjoorary,  deciduous 
or  7nilk  teeth,  as  they  are  called,  begins  at  about  the 
seventh  month  and  is  completed  by  the  twenty-fourth  or 
thirtieth  month. 

The  2^eriods  of  the  eruption  of  the  temporary  teeth  are  as 
follows:  at  about  the  seventh  month,  the  central  incisors; 
at  about  the  seventh  to  tenth  month,  the  lateral  incisors; 
at  about  the  twelfth  to  fourteenth  moiith,  the  first  molars; 
at  about  the  fourteenth  to  twentieth  month,  the  canines; 
at  about  the  eighteenth  to  twenty-fourth  month,  the  sec- 
ond molars.  The  second  molars  often  appear  as  late  as  the 
third  year.  The  upper  teeth  generally  precede  those  of 
the  lower  jaw. 

The  development  of  the  temporary  teeth  begins  at  about 
the  following  periods:  seventh  week,  the  first  molars; 
eighth  week,  the  canines;  ninth  week,  the  incisors;  tenth 
week,  the  second  molars. 

The  permanent  set  consists  of  32  teeth,  16  in  each  jaw. 
They  are  enumerated  from  the  front  as  follows  :  2  cen- 
tral incisors,  2  lateral  incisors,  2  canines,  4  bicuspids,  6 
molars.  The  eruption  of  the  permanent  teeth  begins  at 
about  the^ixth  year  and  is  completed  by  the  twenty- first 
to  the  twenty-fifth  year. 

The  periods  of  the  eruption  of  the  permanent  teeth  are 
as  follows  :  at  the  sixth  year,  the  first  molars  ;  at  the  sev- 
enth year,  the  central  incisors  ;  at  the  eighth  year,  the 
lateral  incisors  ;  at  the  ninth  year,  the  first  bicuspids  ;  at 
the  tenth  year,  the  second  bicuspids  ;  at  the  eleventh  to 
twelfth  year,  the  canines  ;  at  the  twelfth  to  thirteenth 
year,  the  second  molars  ;  at  the  seventeenth  to  twenty- 
fifth  year,  the  third  molars  or  wisdom  teeth. 

The  development  of  the  permanent  teeth  begins  before 
the  development  of  the  temporary  set  is  completed. 


104     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  permanent  set  consists  of  those  teeth  which  succeed 
the  20  temporary  teeth. 

The  permanent  teeth  succeeding  the  temporary  set  are 
the  incisors,  the  canines,  and  the  bicuspids  which  take 
the  place  of  the  molars  of  the  temporary  set. 

The  development  of  these  20  teeth  begins  before  the 
ridges  of  the  dentinal  groove  become  obliterated.  At  about 
this  time  there  appears  an  indentation  or  depression  at  the 
inner  wall  of  the  neck  of  the  tooth-sacs  of  the  temporary 
teeth.  These  indentations  result  in  the  formation  of  a 
secondary  derital  ridge  and  dented  groove  ov  furrow,  and  in 
this  there  develop  the  enamel-organs  and  papillae  for  the 
permanent  teeth;  tliese  structures  also  become  surrounded 
by  a  tooth-sac.  These  permanent  teeth  develop  near  the 
inner  wall  of  the  alveolar  portion  of  the  temporary 
teeth. 

The  superadded  permanent  teeth — namely,  the  three  mo- 
lars in  each  lateral  half  of  the  jaw— develop  successively 
from  the  tooth  in  front.  The  manner  of  their  develop- 
ment is  about  as  follows  :  From  the  enamel-organ  of  the 
second  temporary  molar  a  backward  extension  forms, 
which  becomes  separated,  and  from  which,  at  about  the 
fourth  month  after  birth,  the  enamel-organ  for  the  first 
permanent  molar  develops  ;  from  this,  at  about  the  seventh 
month,  the  enamel-organ  for  the  second  molar,  and  from 
this  again,  at  about  the  third  year,  the  enamel- organ  for 
the  third  molar,  are  developed  in  a  similar  manner.  The 
papillae  and  other  structures  of  the  permanent  teeth  de- 
velop like  those  of  the  temporary  teeth. 

The  eruption  of  the  teeth  begins  when  calcification  is 
sufficiently  completed  to  stand  the  pressure  which  causes 
their  eruption. 

The  alveoli  are  formed  by  an  ossification  of  the  fibrous 
septa  between  the  developing  teeth.  Fibrous  septa,  which 
afterward  ossify,  are  situated  between  the  developing  tem- 


MASTICATION.  105 

porary  and  permanent  teeth,  and  also  between  those  al- 
ready formed. 

The  developing  permanent  teeth  press  against  these  septa, 
causing  their  absorption.  Finally  the  alveolar  portion  of 
the  temporary  teeth  becomes  eroded  and  absorbed  as  a  re- 
sult of  the  pressure  of  the  developing  permanent  teeth. 
During  this  period  numerous  multinuclear  cells,  resembling 
leucocytes,  are  developed  near  the  alveolar  portion  of  the 
temporary  teeth.  They  are  called  odontoclasts,  and  are 
believed  to  play  an  important  role  in  the  absorption  or  car- 
rying-off  of  the  particles  of  inorganic  material  from  the  os- 
seous septa  and  the  alveolar  portion  of  the  temporary  teeth. 
These  become  loosened  through  this  process,  and  are  finally 
shed  to  make  room  for  the  permanent  teeth. 

The  importance  of  the  teeth  as  essential  organs  of 
digestion  is  well  known  to  the  physician  and  the  den- 
tal surgeon,  but  perhaps  not  sufficiently  recognized  and 
understood  by  people  in  general.  It  is  a  frequent  oc- 
currence that  improper  mastication  of  the  solid  foods  is 
the  cause  of  many  ailments,  such  as  digestive  disorders, 
anaemia,  debility,  malnutrition,  headaches,  etc.,  all  of 
which  result  from  an  insufficient  digestion  of  the  im- 
properly masticated  food.  Improper  mastication  is  some- 
times a  bad  habit,  but  often  it  is  caused  by  an  improper 
condition  or  total  absence  of  teeth.  The  teeth,  like  any 
other  structures  in  the  body,  are  subject  to  disease,  mal- 
formation, and  improper  development.  It  is  the  aim  of 
the  dental  surgeon  to  treat  the  diseased  teeth  and  remedy 
any  deficiencies  by  prostheses  and  other  means;  but,  more 
than  this,  it  is  the  duty  and  aim  of  the  dental  practitioner 
to  treat  conditions  which  lead  to  maldevelopment  or  irreg- 
ularities of  teeth,  and  to  prevent  the  decay  of  the  teeth  by 
prophylactic  measures.  Caries  is  probably  the  most  fre- 
quent disease  of  the  teeth ;  it  is  principally  due  to  bacteria, 
for  the  development  of  which  the  buccal  cavity,  if  not  kept 
constantly  in  a  clean  condition,  presents  a  favorable  field. 


106       LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Drugs,  especially  acids  and  caustics,  which  are  given  as 
medicines,  are  often  the  causes  of  diseases  of  the  teeth,  and 
therefore  care  should  be  taken  in  their  administration. 
They  should  either  be  given  in  capsules  or,  when  liquid, 
taken  through  a  glass  tube. 


LEOTUEE  XIll. 

DIGESTION  {continued). 
3.  Insalivation. 

By  the  term  insalivation  we  understand  the  mixing  of 
food  with  the  secretions  of  the  glands  of  the  mouth. 

The  glands  of  the  month  are: 

(a)  The  sahvary  glands— ^.e.,  2  parotids,  2  sublingual, 
and  2  submaxillary. 

(6)  The  mucous  glands,  situated  in  the  mucous  mem- 
brane of  the  cheeks  and  lips. 

(c)  The  glands  of  the  tongue. 

The  SALIVARY  GLANDS  are  oi  the  compound  racemose  or 
tubular  racemose  variety.  They  consist  of  a  duct  and 
a  secreting  portion;  the  latter  consists  of  the  tubular  rami- 
fications of  the  duct,  and  each  of  these  terminates  in  a 
pouch-like  expansion,  the  alveolus,  which  gives  to  the 
gland  a  lobular  appearance. 

The  duct,  the  tubules,  and  the  alveoli  have  one  continu- 
ous basement  membrane,  which  is  lined  with  epithelial 
cells;  in  the  secreting  portion  of  the  gland  these  are  gland- 
ular; in  the  duct,  flat  or  columnar  cells. 

The  salivary  glands  are  divided  into  three  classes: 

(a)  The  true  salivary  glands. 

(6)  The  mucous  salivary  glands. 

(c)  The  mixed  or  muco- salivary  glands. 

The  true  salivary  glands.  In  this  variety  the  alveoli  are 
smaller  than  in  the  others;  they  are  lined  with  nucleated 
glandular  cells,  which  have  an  intranuclear  network  and 
a  granular  protoplasm  ;  they  secrete  a  watery  fluid  con- 
taining serum-albumin,  and  the  alveoli  are  therefore  called 
serous  alveoli.     The  smaller  tubules  of  these  glands  are 


108   LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

lined  with  pavement,  the  main  duct  with  columnar,  epi- 
thelium.     The  parotids  are  glands  of  this  variety. 

The  mucous  salivary  glands  secrete  a  ropy,  viscid  fluid 
which  contains  mucin. 

The  alveoli  of  the  glands  of  this  variety  are  called  mucous 
alveoli.  They  are  larger  than  those  of  the  former  variety, 
and  they  are  lined  by  two  kinds  of  epithelial  cells,  the  cen- 
tral or  nmcous  cells;  they  are  nucleated,  and  have  a  fibril- 
lar network  and  a  transparent  protoplasm  called  mucigen, 
which,  during  the  activity  of  the  cell,  is  converted  into 
mucin.  Scattered  between  these  are  the  marginal  cells; 
they  are  semi-lunar;  their  protoplasm  is  granular  and  con- 
tains no  mucigen.  The  cells  lining  the  alveoli  of  the 
glands  of  this  variety  do  not  completely  fill  the  lumen  of 
the  alveoli.  The  smaller  tubules  are  lined  with  granular 
cells,  the  ducts  with  large,  cylindrical,  nucleated  epithelial 
cells  which  are  finely  striated  toward  the  periphery  and 
transparent  toward  the  centre.  The  sublingual  glands  are 
of  this  variety.  The  mixed  or  inuco-salivarij  glands  liave 
both  serous  and  mucous  alveoli.  The  human  submaxillary 
glands  are  of  this  variety. 

The  parotid  glands  are  the  largest  of  the  salivary  glands. 
They  are  situated  in  front  and  below  the  external  ear,  be- 
neath the  skin  and  subcutaneous  fascia.  A  parotid  gland 
weighs  from  one-half  to  one  ounce  and  has  one  duct,  called 
Stend^s  or  Stenson's  duct,  which  is  the  size  of  an  ordinary 
crow's  quill  and  is  about  2|^  inches  long;  it  opens  on  the 
inner  surface  of  the  cheek  opposite  the  second  molar  of 
the  upper  jaw. 

The  submaxillary  glands  are  situated  in  the  anterior  part 
of  the  submaxillary  triangle,  resting  in  a  shallow  depres- 
sion on  either  side  of  the  inner  surface  of  the  body  of  the 
lower  jaw.  A  submaxillary  gland  weighs  about  two 
drachms  and  has  one  duct,  called  Wharton's  duct;  this  is 
smaller  than  the  duct  of  the  parotid,  being  about  2 
inches  long,  and  opens  on  the  side  of  the  frenulum  linguae. 


INSALIVATIOX.  109 

The  suhJingval  gJands,  two  in  number,  are  situated  be- 
neath the  mucous  membrane  of  the  floor  of  the  mouth  on 
•either  side  of  the  frenukun  hugua?.  A  subhngual  gland 
weighs  about  one  drachm,  is  aknond-shaped.  and  has  from 
ten  to  twenty  fine  ducts,  caUed  the  duds  of  Rivini:  they 
open  at  the  floor  of  the  mouth.  Some  of  these  ducts  also 
unite  and  form  one  duct,  the  duct  of  Bartholin,  which 
opens  into  Wharton's  duct. 

The  salivary  glands  are  supplied  with  lyuiphcdics,  blood- 
vessels, and  nerves;  these  structures  enter  and  emerge  at 
the  hflus  of  the  glands.  The  hlood-supply  of  the  salivary 
glands  is  as  follows: 

The  parotids  receive  blood  through  branches  from  the 
external  carotid  arteries. 

The  submaxillary  glands,  through  branches  from  the 
facial  and  lingual  arteries. 

The  sublingual  glands,  through  branches  from  the  sub- 
lingual and  submental  arteries. 

The  nerve-supply  to  the  salivary  glands  is  as  follows: 

The  parotids  are  supplied  by  branches  from  the  carotid 
plexus  of  the  sympathetic  nerve,  by  branches  from  the 
seventh  cranial  or  facial  nerve,  and  by  a  branch  from  the 
auriculo  temporal  branch  of  the  flfth  cranial  nerve.  Occa- 
.sionally  branches  from  the  great  auricular  nerve  of  the 
cervical  plexus  are  distributed  to  the  gland. 

The  submaxillary  salivary  glands  are  supplied  by  branches 
from  the  submaxillary  ganglion,  which  receives  branches 
from  the  seventh  cranial  nerve  through  the  chorda  tym- 
pani,  from  the  gustatory  branch  of  the  fifth  cranial  nerve, 
and  from  the  sympathetic  nerve. 

The  sublingual  giaiids  are  supplied  by  branches  from  the 
gustatory  of  the  fifth  and  by  branches  from  the  seventh 
cranial  nerve  through  the  chorda  tympani.  and  also  by 
branches  from  the  sympathetic  nerve. 

The  nerves  supplying  the  salivary  glands  are  divided  into 
vasomotor  fibres,  which  terminate  in  the  walls  of  the  blood- 


110    LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

vessels  and  regulate  their  calibre,  and  into  secretory  fibres, 
which  pass  between,  and  terminate  in,  the  glandular  cells 
of  the  glands. 

The  MUCOUS  GLANDS  are  compound  tubular  glands  :  their 
secretion  is  viscid  and  contains  mucin;  their  duct  is  lined 
with  cylindrical  epithelium. 

The  GLANDS  OF  THE  TONGUE  are  also  compound  tubular 
glands.  Weber's  glands,  which  are  situated  near  the  root 
of  the  tongue,  are  raucous;  the  glands  situated  near  the 
circumvallate  papillae  of  the  tongue  are  serous;  and  those 
situated  near  the  tips  of  the  tongue  are  mixed. 

The  secretions  of  the  individual  glands  of  the  mouth 
differ.  The  secretion  of  the  parotid  glands  is  clear,  but  be- 
comes turbid  on  standing.  Its  specific  gravity  is  1003:  it 
consists  of  1^  per  cent  of  sohds  and  of  water.  The  prin- 
cipal organic  \D.gvediien.t\sptyalin;  albumin  and  traces  of 
urea  are  also  found.  The  inorganic  ingredients  are  water, 
bicarbonate  of  potassium,  sodium  and  potassium  chloride, 
and  sulphates  and  traces  of  sulphocyanide  of  potassium  or 
sodium.  Its  physiological  or  diastatic  action  is  more  pow- 
erful than  that  of  the  other  salivary  glands. 

The  secretion  of  the  submaxillary  glands  is  more  viscid 
than  that  of  the  parotids,  owing  to  the  fact  that  it  contains 
mucin;  it  contains  less  ptyalin  than  the  secretion  of  the 
parotids.  It  contains  about  ^  to  1  per  cent  of  solids  and 
99  per  cent  of  water.  The  organic  ingredients  are  ptyalin, 
mucin,  and  epithelial  ceUs.  The  inorganic  ingredients  are 
water,  sodium,  potassium,  and  calcium  chloride,  and  traces 
of  the  sulphocyanide  of  potassium. 

The  secretion  of  the  sublingual  glands  is  strongly  alkaline 
in  reaction;  it  is  very  viscid  and  contains  mucin,  sahvary 
corpuscles,  and  also  traces  of  sulphocyanide  of  potassium. 
It  contains  no  ptyalin,  and  hence  possesses  little  or  no  dia- 
static properties. 

The  secretion  of  the  mucous  glands  contained  in  the 
mucous  membrane  of  the  cheeks  and  hps,  and  that  of  the- 


INSALIVATION.  Ill 

glands  of  the   tongue,  is  alkaline   and  viscid;  it   contains 
water,  salts,  albuminous  matter,  mucin,  but  no  ptyalin. 

The  secretion  of  the  salivary  glands  is  called  saliva.  The 
mixed  saliva  in  the  mouth  contains  the  secretions  of  all 
the  glands  of  the  mouth.  The  physical  properties  of  mixed 
saliva  are  as  follows:  it  is  colorless,  odorless,  and  viscid:  it 
has  an  alkaline  reaction  and  a  specific  gravity  of  1i'mj5  to 
1009. 

The  amount  of  saliva  secreted  in  twenty-four  hours  by 
the  healthy  human  adult  varies  greatly  :  it  may  be  esti- 
mated to  be  from  200  to  1,000  or  even  2,000  grammes — 
that  is.  from  7  to  50  or  TO  ounces. 

The   chemical   coniposition    of   mixed   human   saliva   is 
about  as  follows: 
.  Water,  995  parts  in  1,000. 

Organic  ingredients,  2.5  to  3.5  in  l.uOO. 

Inorganic  solids,  1.5  to  2.5  in  1,000. 

The  organic  ingredients  of  the  sahva  are:  mucin,  serum- 
albumin,  ptyahn,  epithelial  cells,  and  sahvary  corpuscles. 

Mucin  is  the  most  abundant,  ptyalin  the  most  important, 
organic  ingredient  of  the  sahva:  the  latter  is  a  ferment, 
giving  to  the  saliva  its  diastatic  prof)erty. 

The  inorganic  sohds  are  the  salts,  namely,  sodium  and 
potassium  chloride,  phosphate  of  calcium,  magnesium,  and 
sodium,  and  traces  of  sulphocyanide  of  potassium  and 
sodium. 

A  microscopical  examination  of  the  sahva  reveals  the 
fact  that  it  contains  bodies  which  are  not  actual  but  acci- 
dental ingredients.  These  are:  1.  Large,  lounded.  nucle- 
ated cellular  elements,  caUed  salivary  corpuscles ;  they 
originate  in  the  salivary  glands. 

2.  Epithelial  cells  from  the  mucous  membrane  of  the 
mouth  and  tongue. 

3.  Micro-organisms,  such  as  the  leptothrix  buccalis,  the 
bacillus  buccalis,  the  spirihum  sputigenum,  and  the  spiro- 
chaete  dentium. 


112       LECTURES   OX   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  buccal  cavity,  especially  the  spaces  between  the 
teeth,  and  cavities  of  teeth  in  which  particles  of  food  are 
retained,  are  a  favorable  field  for  the  growth  and  develop- 
ment of  these  micro-organisms,  most  of  which  are  dele- 
terious and  often  cause  the  decay  of  the  teeth.  Frequent 
cleaning  of  the  mouth  and  teeth,  and  the  use  of  antiseptic 
mouth  washes,  prevent  their  development. 

The  physiological  actions  and  uses  of  the  saliva  may  be 
enumerated  as  follows: 

1.  It  has  a  diastatic  action,  producing  chemical  changes 
in  starchy  foods. 

2.  It  moistens  the  food,  dissolves  portions  of  the  food, 
and  assists  in  the  formation  of  the  bolus. 

3.  It  aids  articulation  and  deglutition. 

4.  It  stimulates  the  gastric  secretion. 

The  diastatic  action  of  the  saliva  is  a  chemical  one. 
Starch  {CJ^.^O.j  consists  of  granules  which  are  composed 
of  cellulose  and  granulose.  Starch  granules  are  insoluble 
in  cold  water;  when  boiled  the  cellulose  is  broken  up  and 
the  liberated  granulose  forms  a  paste.  Unbroken  starch 
granules  are  not  easily  acted  upon  by  the  saliva.  Starch 
paste,  when  brought  in  contact  with  saliva,  soon  becomes 
liquefied  and  transparent.  The  change  which  takes  place 
is  a  chemical  one,  and  it  consists  in  the  transformation  of 
the  starch  into  dextrin,  and  if  the  action  of  the  saliva  is 
continued  the  dextrin  is  transformed  into  a  sugar  called 
maltose.  During  the  transformation  of  starch  into  dextrin 
two  varieties  of  the  latter  are  produced — namely,  erythro- 
dextrin  and  achroodextrin.  Dextrin  has  the  same  chemi- 
cal formula  as  starch,  but  differs  in  its  physical  proper- 
ties. Starch  exists  in  granules,  dextrin  is  obtained  as  an 
amorphous  powder.  Starch  is  not  soluble  in  cold  water, 
while  dextrin  is  freely  soluble  in  the  same.  Starch  with 
iodine  gives  a  blue  color,  erythrodextrin  a  rose,  while 
achroodextrin  has  no  color  reaction 

Maltose  (C,3q-20,,)  is  a  sugar  which  differs  from  grape- 


INSALIVATION.  113 

sugar  in  that  it  contains  one  molecule  of  water  less  than 
glucose,  and  in  that  its  power  to  reduce  metallic  salts,  such 
as  cupric  sulphate,  is  less  than  that  of  grape-sugar.  The 
chemical  tests  for  maltose  are,  first,  Moore's  or  Trommer's 
test,  which  consists  in  the  addition  of  liquor  kali  caustici 
to  the  solution ;  the  presence  of  maltose  is  indicated  by  a 
brown  discoloration  w^hen  the  solution  is  boiled.  Second, 
the  test  wath  Fehling's  solution. 

The  diastatic  action  of  the  saliva  is  due  to  ptyalin. 
Ptyalin  is  an  organic  nitrogenous  substance  belonging  to 
the  class  of  ferments.  It  can  be  obtained  from  the  saliva 
in  the  following  manner:  first  the  saliva  is  acidulated 
with  phosphoric  acid,  then  lime-water  is  added  until  a  pre- 
cipitate of  calcium  carbonate  is  obtained,  and  with  this  the 
ptyalin  will  be  precipitated.  The  ptyalin,  being  soluble 
in  water,  can  be  washed  out  from  the  precipitated  calcium 
carbonate,  and  then  it  is  precipitated  from  its  watery  solu- 
tion by  alcohol.  Ptyalin  so  obtained  is  a  white,  amor- 
phous powder. 

The  nervous  mechanism  of  the  secretion  of  the  saliva. 
The  secretion  of  saliva  is  a  reflex  nervous  act.  When  food 
is  introduced  into  the  mouth,  the  stimulus  is  couveyed  by 
the  sensory  nerves  of  the  buccal  cavity  to  the  centre  of 
insalivation,  which  is  situated  in  the  medulla  oblongata; 
from  this  centre  the  stimulus  is  conveyed  to  the  secretory 
and  vasomotor  nerve-fibres  which  are  distributed  to  the 
sahvary  glands.  Stimulation  of  the  seventh  cranial  nerve 
and  of  the  chorda  tympani  produces  a  profuse  flow  of  a 
watery  secretion,  especially  from  the  submaxillary  and 
the  sublingual  salivary  glands,  and  the  vessels  of  these 
glands  become  dilated.  Stimulation  of  the  sympathetic 
nerve  produces  a  scanty  secretion  from  these  glands. 
These  facts  demonstrate  that  the  seventh  cranial  nerve 
and  the  chorda  tympani  supply  to  these  glands  principally 
secretory  and  vasodilator  fibres,  whereas  the  sympathetic 
nerve  supplies  to  them  secretory  and  vasoconstrictor  fibres. 


114      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

Stimulation  of  the  sympathetic  nerve  does  not  excite  the 
secretion  from  the  parotid  salivary  gland.  Stimulation 
of  the  glosso-pharyngeal  nerve,  which  sends  branches  to 
the  parotid  through  the  otic  ganglion,  produces  a  thick 
secretion.  Stimulation  of  the  facial,  which  also  sends 
fibres  through  the  otic  ganglion  to  the  parotid,  produces 
a  profuse  watery  secretion  from  that  gland.  Stimulation 
of  other  more  distant  nerves — for  instance,  of  the  pneumo- 
gastric— also  stimulates  or  excites  the  secretion  of  saliva. 

Ordinarily  the  secretion  of  saliva  is  excited  by  mechani- 
cal, chemical,  or  electrical  stimuli  applied  to  the  sensory 
nerves  of  the  mucous  membrane  lining  the  mouth. 

Introduction  of  food  into  the  mouth,  mastication,  and 
the  chewing  of  substances  are  the  common  causes  of  the 
flow  of  saliva.  It  is  often  excited  simply  by  seeing  or 
smelling  articles  of  food,  or  even  by  thinking  of  them.  Di- 
rect stimulation  of  the  centre  of  insalivation  in  the  medulla 
oblongata  excites  the  flow  of  saliva.  When  the  cerebral 
nerves  supplying  the  salivary  glands  are  severed,  a  continual 
secretion  takes  place  for  several  days  until  a  degeneration 
of  the  gland  or  glands  has  occurred.  This  condition  is 
called  paralytic  secretion  of  saliva.  Certain  drugs — for 
instance,  atropine  and  curare — also  the  stimulation  of  cer- 
tain sensory  nerves,  inhibit  the  secretion  of  saliva.  Other 
drugs — such  as  mercurial  preparations,  pilocarpine — cause 
an  excessive  flow  of  saliva,  a  condition  which  is  called 
ptyalism.  Diseases,  ulcers,  and  inflammation  of  the  mu- 
cous membrane  of  the  mouth,  also  neuralgia,  cause  an 
increased  flow  of  saliva. 

The  mode  of  the  secretion  of  saliva,  and  the  changes 
which  take  place  in  the  glands — e.g.,  in  their  histological 
elements — may  be  described  as  follows  :  The  ingredients  of 
the  saliva  do  not  all  exist  as  such  in  the  blood  conveyed  to 
the  gland,  but  are  produced  by  the  cells  of  the  gland  from 
materials  of  the  blood.  It  has  been  observed  that  the 
glandular  cells  lining  the  serous  alveoli  become  larger  and 


INSALIVATION.  115 

distended  during  the  period  of  rest,  and  also  that  their  pro- 
toplasm during  this  time  becomes  more  granular.  During 
the  active  period  or  stage  of  secretion  the  gland  and  its 
granular  protoplasm  diminish.  The  theory  is  that  these 
cells  transform  materials  of  the  blood  into  their  protoplasm, 
and  that  this  transforms  itself  into  the  ingredients  of  the 
saliva,  v^hich  are  not  previously  found  in  the  blood. 

The  changes  observed  in  the  glandular  cells  lining  the 
mucous  alveoli  consist  in  a  swelling  of  their  protoplasm 
during  the  stage  of  rest.  The  protoplasm  of  these  cells  is 
transformed  into  mucigen,  which,  during  secretion,  is  trans- 
formed into  mucin. 

The  secretion  of  saliva  during  the  first  two  months  of 
infantile  life*  is  very  scanty,  and  the  saliva  at  this  period 
possesses  but  little  diastatic  property.  Infants  at  this  age 
should  for  this  reason  receive  no  amylaceous  food.  After 
the  second  month  the  secretion  becomes  more  copious.  It 
is  very  much  increased  during  dentition,  owing  to  the  irri- 
tation of  the  mucous  membrane  of  the  mouth. 

It  has  been  found  that  in  a  disease  called  thrush  the 
saliva  possesses  no  diastatic  action.  Thrush  is  a  disease 
characterized  by  a  whitish  deposit  on  the  tongue,  gums, 
and  mucous  membrane  of  the  mouth  as  the  result  of  the 
development  of  a  vegetable  micro-organism.  The  disease 
occurs  in  infants  as  the  result  of  insufficient  cleansing  of 
the  mouth.  Tea  has  the  property  of  decreasing  or  de- 
stroying the  diastatic  action  of  the  saliva.  It  is  for  this 
reason  that  it  is  more  desirable  to  drink  tea  after  than 
during  meals. 


LEOTUEE  XIY. 

DIGESTION  {continued). 

4.  Deglutitio7i. 

When  the  food  is  masticated  and  insalivated  the  bolus 
is  collected  upon  the  tongue  and  transmitted  by  muscular 
action  into  the  pharynx,  and  from  this  through  the  oeso- 
phagus into  the  stomach.  The  whole  process  is  called  deg- 
lutition, or  swallowing. 

Deglutition  is  a  muscular  act,  and  the  organs  concerned 
in  it  are  the  tongue,  the  soft  palate,  the  pharynx,  and  the 
oesophagus. 

The  tongue  is  a  conical-shaped  muscular  organ  situated 
in  the  floor  of  the  mouth,  its  base  at  the  posterior  part  of 
the  floor  of  the  mouth  ;  its  apex  protrudes  forward.  The 
free  surface  is  covered  with  mucous  membrane.  The  main 
mass  of  the  organ,  is  composed  of  fibres  of  the  lingualis 
muscle,  which  are  inserted  in  a  septum  which  passes  ver- 
tically from  the  apex  to  the  base  of  the  tongue,  separating 
it  into  halves.  The  fibres  of  the  lingualis  muscle  blend 
with  those  of  the  extrinsic  muscles  and  pass  in  a  trans- 
verse and  vertical  direction.  The  delicate  motions  of  the 
tongue  are  produced  by  the  contractions  of  the  fibres  of 
the  lingualis  muscle.  The  intrinsic  muscles  are  the  genio- 
hyoglossus,  the  hyoglossus,  the  styloglossus,  and  the  pala- 
to-glossus,  one  of  each  on  either  side. 

The  genio-hyoglossus  arises  from  the  superior  genial 
tubercles,  and  from  this  point  its  fibres  expand  in  a  fan- 
like manner  and  are  inserted  in  the  under-surface  of  the 
tongue  ;  the  posterior  fibres  pass  to  the  hyoid  bone.  Con- 
traction of  the  anterior  fibres  causes  protrusion  of  the  tip 
of  the  tongue;  contraction  of  the  posterior  fibres  causes 


DEGLUTITION.  117 

retraction  of  the  tongue;  and  contraction  of  the  fan-like 
expanded  fibres  makes  the  tongue  concave  from  side  to 
side,  forming  a  channel  through  which  liquids,  by  suction, 
pass  to  the  pharynx. 

The  hyoglossus  arises  from  the  hyoid  bone.  Its  fibres 
are  inserted  in  the  sides  of  the  tongue,  and  their  contrac- 
tion draws  the  sides  of  the  tongue  down,  thus  making  its 
surface  convex  from  side  to  side. 

The  styloglossus  arises  from  the  styloid  process  of  the 
temporal  bone,  and  its  fibres  are  attached  posteriorly  to 
the  sides  of  the  tongue.  Contraction  of  these  fibres  draws 
the  base  of  the  tongue  upward  and  backward. 

The  palatoglossus  muscles  form  the  anterior  pillars  of  the 
soft  palate  ;  their  action  is  similar  to  that  of  the  stylo- 
glossus. The  mucous  membrane  is  covered  with  stratified 
epithelium.  Beneath  the  mucous  membrane  are  numerous 
secreting  glands,  which  open  on  the  surface  of  the  tongue, 
the  secretions  of  which  mix  with  that  of  the  other  glands 
of  the  mouth. 

From  the  mucous  surface  of  the  tongue  are  projected 
numerous  papillae,  which  are  organs  of  the  special  sense  of 
taste. 

The  motor  nerves  of  the  tongue  are  branches  from  the 
hypoglossal  or  twelfth  cranial  nerves  which  are  distributed 
to  the  extrinsic  muscles,  and  branches  from  the  seventh 
cranial  nerve  through  the  chorda  tympani  which  are  dis- 
tributed to  the  fibres  of  the  lingualis  muscle.  The  tongue 
assists  in  the  act  of  mastication  by  conveying  the  food  be- 
tween the  teeth.  It  also  assists  in  the  insalivation  of  the 
food  by  its  various  motions.  In  the  act  of  deglutition  its 
motions  are  most  important. 

The  functions  of  the  tongue  as  an  organ  of  special  sense 
I  will  describe  later. 

The  soft  palate  is  suspended  from  the  posterior  border  of 
the  hard  palate.     It  forms  the  arched  roof  of  the  posterior 


118    LECTURES   OX   HUMAN   PHYSIOLOGY'   AND    HISTOLOGY. 

part  of  the  buccal  cavity,  and  au  incomplete  septum  be- 
tween the  buccal  and  pharyngeal  cavities. 

The  soft  palate  is  composed  of  a  central  tendinous  por- 
tion and  five  muscles  on  each  side.  The  free  surfaces  are 
covered  with  mucous  membrane;  that  of  the  lower,  or 
buccal  surface,  is  covered  with  stratified  squamous  epi- 
thelium :  that  of  the  upper  surface — viz..  that  which  is 
directed  toward  the  respiratoiy  passages — is  covered  with 
ciliated  epithelium. 

The  five  pairs  of  muscles  of  the  soft  palate  are:  the  ten- 
sores  palati,  the  levatores  palati,  the  azygos  uvula?,  and 
the  palato-glossus  muscles,  forming  the  anterior  pillars, 
and  the  palato-phaiyngeus  muscles,  forming  the  posterior 
pillars.  The  space  between  the  pillars  is  called  the  isth- 
mus of  the  fauces. 

The  action  of  these  muscles  is  of  the  greatest  importance 
in  the  first  stage  of  the  act  of  deglutition.  To  some  extent 
the  name  of  these  muscles  explains  their  action. 

The  motor  nerves  to  the  muscles  of  the  soft  palate  are 
branches  received  through  Merkel's  ganglion  and  through 
the  otic  ganglion. 

The  pharyn.r  is  a  musculo-membranous  sac.  conical  in 
shape,  with  its  base  directed  upward  and  its  apex  directed 
downward.  It  is  about  4^  inches  long,  and  broader  in  its 
transverse  than  in  its  antero-posterior  diameter.  It  is  at- 
tached above  to  the  sphenoid  bone  and  to  the  basilar  pro- 
cess of  the  occipital  bone  :  posteriorly  it  is  attached  to  the 
cervical  vertebrae  ;  below  it  is  continuous  with  the  oesopha- 
gus ;  laterally  it  is  attached  to  the  styloid  processes  of  the 
temporal  bone,  and  in  front  to  the  larynx,  hyoid  bone, 
tongue,  to  the  inferior  maxillary  bone,  and  to  the  pterygoid 
process  of  the  sphenoid  bone. 

The  pharynx  is  composed  of  three  coats — an  internal  mu- 
cous, a  middle  muscular,  and  an  external  fibrous.  The 
mucous  membrane  of  the  pharynx  is  covered  above  the  soft 
palate  with  ciliated,  columnar,  and  below  the  soft  palate 


DEGLUTITION.  119 

by  squamous,  epithelium.  The  pharynx  communicates  by 
seven  openings  with  the  nasal,  aural,  and  buccal  cavities, 
and  with  the  larynx  and  the  cesophagus. 

The  muscles  of  the  pharynx  are  the  superior,  inferior, 
and  middle  constrictors,  and  the  stylo-pharyngeus  and 
palato-pharyngeus  on  each  side.  The  action  of  the  con- 
strictors is  the  contraction  upon  the  bolus,  thus  forcing  it 
into  the  oesophagus.  The  action  of  the  stylo-pharyngeus 
and  palato-pharyngeus  is  the  raising  of  the  pharynx. 

The  motor  nerves  supply iag  the  pharyngeal  muscles  are 
branches  from  the  tenth  cranial  or  pueumogastric  nerves. 

The  oesophagus,  or  gullet,  is  a  musculo-membranous  tube 
about  9  inches  long.  It  extends  from  the  space  between 
the  fifth  and  sixth  cervical  vertebrse  to  the  ninth  dorsal 
vertebra.  It  is  situated  in  front  of  the  spinal  column, 
passes  through  the  neck  into  the  thoracic  cavity,  in  which 
it  descends  through  the  posterior  mediastinum,  then 
passes  through  an  opening  in  the  diaphragm,  and  termi- 
nates at  the  cardiac  opening  of  the  stomach.  The  oesopha- 
gus has  also  three  coats — namely,  an  external  muscular,  a 
middle  fibrous  or  areolar,  and  an  internal  or  mucous.  The 
latter  is  arranged  in  longitudinal  folds  and  is  covered  with 
stratified  pavement  epithelium.  Beneath  the  mucous  coat 
are  a  layer  of  non-striated  muscular  fibres  and  a  number  of 
glands. 

The  muscular  coat  consists  of  an  external  layer  of  longi- 
tudinally arranged  fibres  and  an  inner  layer  of  circular 
fibres.  In  the  upper  part  of  the  oesophagus  the  muscular 
fibres  are  of  the  striated,  voluntary  variety  ;  those  in  the 
lower  part  are  non-striated  and  not  under  the  control  of 
the  will. 

The  motor  nerve  supply  to  the  oesophagus  is  by  branches 
from  the  tenth  cranial  or  pueumogastric  nerves. 

The  act  of  deglutition  consists  of  three  distinct  stages. 
The  first  stage  consists  in  the  transmission  of  the  bolus 


120     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

from  the  nioath  through  the  isthmus  of  the  fauces  into  the 
pharynx.     This  takes  place  in  the  following  manner  : 

1.  The  mouth  is  closed  by  the  contraction  of  the  orbicu- 
laris oris  muscle. 

2.  The  lower  jaw  is  fixed  against  the  upper  jaw  by  the 
contraction  of  the  elevators  of  the  lower  jaw,  and  the 
pharynx,  larynx,  and  hyoid  bone  are  raised. 

3.  The  tongue,  with  the  bolus  upon  its  dorsum,  is  pressed 
against  the  palate,  and  then  the  bolus  is  forced  down  the 
inclined  plane  through  the  isthmus  of  the  fauces  into  the 
pharyngeal  cavity. 

4.  The  anterior  pillars — e.g.,  the  palato-glossus  muscles 
— contract,  and  thus  prevent  the  forcing  back  of  the  bolus 
into  the  buccal  cavity. 

The  upper  opening  of  the  larynx  is  closed,  during  the 
stage  of  deglutition,  by  the  epiglottis,  which  is  pressed 
against  the  opening  by  the  raising  of  the  larynx  and  hyoid 
bone  and  by  the  raising  of  the  root  of  the  tongue.  Par- 
ticles of  food  are  thus  prevented  from  passing  into  the 
larynx. 

The  second  stage  consists  in  the  grasping  of  the  bolus  by 
the  constrictors  of  the  pharynx,  and  the  forcing  of  it  into 
the  oesophagus  by  the  peristaltic  contraction  of  the  con- 
strictors. The  food  is  prevented  from  entering  the  naso- 
pharyngeal cavity  by  the  contraction  and  elevation  of  the 
posterior  pillars  of  the  palato-pharyngeus  muscles,  which 
thus  form  a  septum  between  the  upper  and  lower  part  of 
the  pharynx. 

The  third  stage  of  deglutition  consists  in  the  forcing  of 
the  food  through  the  oesophagus  into  the  stomach  by  the 
peristaltic  contraction  of  the  muscular  fibres  of  the  oeso- 
pliagus,  which  contract  above  the  bolus  and  thus  force  it 
onward. 

Deglutition  is  partly  a  voluntary,  partly  an  involuntary 
nervous  act. 

The  first  stage  is  voluntary,  the  second  and  third  invol- 
untary. 


STOMACH   DIGESTION.  121 

The  centre  of  deglutition  is  located  in  the  medulla  oblon- 
gata. 

The  sensory  nerves  are  branches  from  the  fifth  cranial 
nerve  supplying  the  soft  palate,  branches  from  the  ninth 
cranial  nerve  supplying  the  tongue  and  pharynx,  and 
branches  from  the  sympathetic  nerve. 

The  motor  nerves  are  branches  from  the  fifth,  seventh, 
ninth,  tenth,  and  twelfth  cranial  nerves  supplying  the 
muscles  of  mastication,  and  those  of  the  tongue,  palate, 
pharynx,  larynx,  and  the  oesophagus. 

5.  Stomach  Digestion. 

The  digestive  processes  which  take  place  in  the  stomach 
are  described  as  the  stomach  digestion,  or  the  chymificatioju 

The  stomach  is  the  dilated  portion  of  the  ahmentaiy 
canal  which  is  situated  between  the  lower  end  of  the  oeso- 
phagus and  the  small  intestines.  The  stomach  is  located 
in  the  abdominal  cavity,  occupying  the  region  of  the  epi- 
gastrium, and  extending  transversely  from  the  left  to  the 
right  hypochondrium.  The  stomach  is  about  12  inches 
long  and  4  inches  wide  at  its  widest  part;  it  presents  for 
examination  2  extremities,  the  pyloric  and  the  cardiac:  2 
openings,  the  cardiac  and  the  pyloric  :  2  borders,  the 
upper  and  lower;  and  2  surfaces,  the  anterior  and  poste- 
rior. 

The  cardiac  extremity,  also  called  the  left,  greater,  or 
splenic  extremity,  extends  into  the  left  hypochondrium 
and  is  in  contact  with  the  spleen ;  it  presents  a  pouch-like 
expansion,  which  is  called  the  cardia  or  the  fundus. 

The  pyloric  extremity,  also  called  the  right  or  lesser  ex- 
tremity, is  situated  a  little  to  the  right  of  the  linea  alba, 
behind  the  abdomiual  wall;  it  is  in  contact  with  the  under- 
surface  of  the  liver. 

The  cardiac  or  cesophagecd  opening  of  the  stomach  com- 
municates with  the  oesophagus;  it  has  the  form  of  an  in- 
verted funnel,  and  is  situated  about  1  inch  to  the  left  of 


122       LECTURES   ON  HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

the  sternum,  behind  the  costal  cartilage  of  tiie  seventh 
rib.  The  cardia  of  the  stomach  extends  from  2  to  3  inches 
to  the  left  of  this  opening. 

The  pyloric  opening  communicates  with  the  duodenum 
of  the  small  intestines:  it  is  a  circular  opening  in  the  pylo- 
ric extremity. 

The  upper  border,  also  called  the  lesser  curvature,  is  con- 
cave and  extends  from  the  cardiac  to  the  pyloric  opening. 

The  loiver  or  greater  curvature  is  convex. 

The  anterior  surface  of  the  stomach  is  directed  forward 
and  a  little  upward;  it  is  in  relation  with  the  abdominal 
wall,  with  the  under-surface  of  the  left  lobe  of  the  liver 
and  of  the  diai)hragm. 

The  posterior  surface  is  directed  backward  and  down- 
ward, and  is  in  relation  with  the  pancreas,  the  solar  nerve 
plexus,  and  the  large  abdominal  vessels. 

The  position  of  the  stomach,  and  its  relations  to  the  abdo- 
minal viscera,  vary  with  the  condition  of  the  stomach. 

The  stomach  is  held  in  its  position  by  a  fold  of  perito- 
neum called  the  gastrophrenic  ligament  and  by  the  lesser 
omentum. 

The  walls  of  the  stomach  are  composed  of  four  coats — 
namely,  the  serous,  muscular,  areolar,  and  mucous. 

The  serous  coat  is  derived  from  the  peritoneum;  it  covers 
the  entire  organ,  except  at  the  borders  where  the  omentum 
is  attached. 

The  muscular  coat  consists  of  non-striated  fibres,  which 
are  arranged  longitudinally,  circularly,  and  obliquely. 

The  longitudinal  fibres  are  continuous  with  the  longitu- 
dinal fibres  of  the  oesophagus;  they  spread  over  the  curva- 
tures and  extremities  and  are  continuous  as  the  longitudi- 
nal muscular  fibres  of  the  duodenum. 

The  circular  fibres  are  situated  beneath  the  longitudinal 
fibres  and  surround  in  a  layer  the  whole  organ ;  they  are 
most  abundant  around  the  pylorus,  where  they  protrude 
into  the  lumen  of  the  latter  and  form,  with  the  mucous  cov- 
ering, the  2^ y lor ic  valve. 


STOMACH   DIGESTION.  123 

The  oblique  fibres  pass  obliquely  from  left  to  right  of  the 
oardia  and  whole  splenic  end  of  the  stomach. 

The  contraction  of  the  muscular  fibres  produces  the 
peristaltic  movements  of  the  stomach,  by  which  its  con- 
tents are  well  mixed  with  the  gastric  juice  and  are  trans- 
mitted through  the  pyloric  opening  into  the  duodenum. 

The  areolar  coat  is  situated  between  the  muscular  and 
1;he  mucous  coats;  it  serves  to  support  the  blood-vessels  of 
the  stomach,  and  is  also  called  its  vascular  coat. 

The  mucous  coat  of  the  stomach  is  thrown  into  nume- 
rous longitudinal  folds  called  the  jmgce;  these  become  un- 
folded when  the  stomach  is  distended,  and  its  mucous 
lining  then  presents  a  smooth  surface. 

The  mucous  membrane  of  the  stomach  consists  of  an 
areolar  submucous  coat,  a  layer  of  non-striated  mucous 
fibres  called  the  muscularis  mucosce,  these  covered  by  a 
single  layer  of  columnar  epithelial  cells  resting  upon  a 
delicate  basement  membrane. 

When  examined  under  the  microscope  the  surface  of  the 
mucous  membrane  has  a  velvety  appearance;  it  shows 
many  shallow  depressions,  which  are  called  alveoli;  in  the 
bottom  of  these  are  seen  the  delicate  openings  of  the  se- 
creting glands  of  the  mucous  membrane.  The  alveoli  are 
separated  by  slightly  elevated  ridges. 

The  secreting  glands  of  the  stomach  are  called  gastric 
follicles.  The  human  stomach  has  two  varieties  of  these, 
called  respectively  the  pyloric  and  the  peptic  glands;  they 
differ  in  their  structure,  distribution,  and  secretion. 

The  pyloric  glands  are,  as  the  name  implies,  located  near 
the  pylorus.  They  are  branched,  tubular  glands  consisting 
of  two  or  three  convoluted  tubules  which  open  into  one 
common  duct,  which  is  about  the  same  length  as  the  tu- 
bules. The  gland  consists  of  a  delicate  basement  mem- 
brane, which  is  lined  with  epithelial  cells.  The  duct  and 
mouth  of  these  glands  are  lined  with  a  columnar  epithe- 
lium; the  secreting  portions  of  the  gland — e.g.,  the  tubules 


124       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY, 

— are  lined  with  short  columnar  or  cubical  glandular  epi- 
thelial cells  which  have  a  granular  protoplasm  and  do  not 
occlude  the  lumen  of  the  glands.  The  whole  gland  is 
supported  by  areolar  and  adenoid  tissue,  and  in  its  lower 
portion  is  surrounded  by  fibres  of  the  muscularis  mucosae. 

The  peptic  glands,  or  fundus  glands,  are  most  numerous 
near  the  fundus;  they  consist  also  of  from  three  to  four 
tubules,  which  open  into  one  common  duct.  The  tubules 
in  this  variety  are  not  convoluted,  and  the  duct  is  shorter 
and  only  about  one-third  of  the  length  of  the  tubules. 
The  neck — the  portion  where  duct  and  tubules  join — is  con- 
stricted. The  duct  is  lined  with  columnar  epithelium,  and 
the  secreting  portion  of  the  gland  with  two  kinds  of  cells, 
called  the  parietal  cells  and  the  central  or  chief  cells. 

The  chief  or  central  cells  form  in  a  continuous  layer  the 
inner  lining  of  the  secreting  portion  of  these  glands;  they 
are  short,  cubical,  polyhedral,  or  columnar  nucleated  cells 
which  have  a  granular  protoplasm. 

The  parietal  cells  are  large,  ovoid,  and  nucleated  cells 
and  have  a  granular,  reticulated  nucleus;  they  are  situated 
between  the  layer  of  central  cells  and  the  membrana  pro- 
pria; they  do  not  form  a  continuous  layer,  but,  owing  to 
their  large  size,  cause  a  bulging-out  of  the  basement  mem- 
brane These  cells  are  also  called  the  acid-forming  cells  of 
Langley.  Between  their  tubules,  in  a  submucous  tissue, 
are  collections  of  lymphoid  tissue  which  resemble  the  soli- 
tary glands  of  the  intestines. 

The  blood  supply  of  the  stomach  is  from  branches  of  the 
coeliac  axis,  the  second  branch  of  the  abdominal  aorta,  as 
follows : 

1.  The  gastric  artery. 

2.  The  hepatic  artery,  which  gives  to  the  stomach  the 
pyloric  artery  and  the  arteria  epiploica  dextra. 

3.  The  splenic  artery,  which  gives  to  the  stomach  the 
arteria  epiploica  sinistra  and  the  vasa  brevia.  These  arte- 
ries anastomose  freely  and  supply  the  muscular  coat.    In 


STOMACH   DIGESTION.  125 

the  submucous  coat  they  form  capillary  plexuses  around 
the  tubules  of  the  secreting  glands,  and  then  secondary 
plexuses  are  formed  around  the  necks  and  ducts  of  these 
glands.  From  these  secondary  plexuses  the  veins  arise, 
and,  pursuing  the  same  course  backward,  return  the  blood 
from  the  stomach  by  the  superior  mesenteric  and  splenic 
-veins  into  the  portal  vein. 

The  nerve- supply  of  the  stomach  is  from  the  gastric 
branches  of  the  tenth  cranial  or  pneumogastric  nerve,  and 
from  branches  of  the  solar  plexus  of  the  sympathetic 
nerve.  Plexuses  composed  of  non-medullated  nerve-fibres 
and  ganglion-cells  are  contained  in  the  muscular  and  areo- 
lar coat;  they  are  called  respectively  Auerhacfi's  and  Meiss- 
ner^s  plexus. 

Lymphatics  and  collections  of  adenoid  tissue  are  distrib- 
uted in  the  coats,  especially  in  the  submucous  or  areolar 
coat. 


LECTURE   XY. 

DIGESTION   {continued). 

The  Gastric  Juice. 

The  secretion  of  the  glands  of  the  stomach  is  called  the 
gastric  juice.  Gastric  juice  is  not  secreted  continuously, 
but  only  at  such  times  as  the  mucous  membrane  is  irri- 
tated by  stimuli,  either  chemical,  thermal,  or  mechanical ; 
ordinarily  the  introduction  of  food,  or  even  of  indigestible 
substances,  excites  the  secretion  of  gastric  juice. 

The  quantity  of  gastric  juice  secreted  in  a  certain  time 
varies  greatly.  It  has  been  estimated  that  a  healthy 
human  adult  taking  food  in  proper  quantity  and  quality, 
and  at  regular  Intervals,  secreteis  from  10  to  20  pints  of 
gastric  juice  in  twenty-four  hours. 

The  physical  properties  of  gastric  juice  may  be  said  to  be 
as  follows:  gastric  juice  is  a  clear,  yellowish  liquid,   hav- 
ing a  specific  gravity  of  1010,  a  decided  acid  reaction,  and 
a  peculiar  odor. 
The  chemical  composition  of  gastric  juice  is  as  follows: 
Water,  994.4. 
Inorganic  salts,  2.2. 
Sodium  chloride. 
Potassium  chloride. 
Calcium  chloride. 
Ammonium  chloride. 
Calcium  phosphate. 
Magnesium  phosphate. 
Pepsin,  3.2. 

Free  hydrochloric  acid,  0.2. 
The  water  and  inoi'ganic  salts  pre-exist  as  such  in  the 


THE   GASTRIC   JUICE.  127 

blood  and  are  secreted  by  the  gastric  glands.  Pepsin  and 
hydrochloric  acid  do  not  pre-exist  in  the  blood,  but  are 
formed  by  the  secreting  cells  of  the  gastric  glands. 

Pepsin  is  an  organic  nitrogenized  substance  belonging  to 
the  class  of  ferments.  It  can  be  obtained  by  precipitating 
it  from  its  solution  with  alcohol  or  by  extracting  it  from 
the  stomach  mucous  membrane  with  glycerin. 

Pepsin  is  a  proteolytic  ferment — i.e.,  one  which  causes  a 
change  of  proteids  into  peptones,  but  it  does  so  only  in 
an  acid  medium.  Pepsin  is  formed  from  materials  of  the 
blood  by  the  cells  lining  the  secreting  portions  of  the  fun- 
dus and  pyloric  glands;  in  the  fundus  glands  the  pepsin  is 
formed  in  the  central  or  chief  cells.  The  granular  proto- 
plasm of  the  cells  which  produces  the  pepsin  is  composed 
of  a  substance  called  zymogen  or  propeptone.  It  has  no 
proteolytic  property,  but  is  transformed  into  pepsin  in  the 
presence  of  hydrochloric  acid. 

The  hydrochloric  acid  of  the  gastric  juice  is  formed  from 
sodium  chloride  of  the  blood  by  the  ovoid  parietal  cells  of 
the  fundus  glands.  Its  exact  mode  of  formation  in  these 
cells  is  unknown. 

Maly  showed  that  in  a  mixture  of  lactic  acid  and  chlo- 
rides small  portions  of  hydrochloric  acid  would  form  upon 
the  addition  of  water,  and  this  was  thought  to  explain  the 
presence  of  the  hydrochloric  acid  in  the  gastric  juice.  But 
it  has  been  shown  that  lactic  acid  is  only  an  accidental 
ingredient  of  the  gastric  juice;  it  is  only  formed  in  the 
stomach  as  a  product  of  the  decomposition  of  certain  sub- 
stances, and  its  formation  can  be  prevented  and  still  the 
gastric  juice  will  contain  hydrochloric  acid.  These  facts 
tend  to  disprove  Maly's  theory.  Since  the  discovery  that 
two  kinds  of  secreting  glands  exist  in  the  stomach,  it  has 
been  demonstrated  beyond  a  doubt,  by  Heidenheim  and 
others,  that  the  HCl  is  formed  in  or  by  the  ovoid  parietal 
cells  of  the  fundus  glands  as  the  result  of  their  special 
physiological  property.     Gastric  juice,  as  taken  from  the 


128       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

stomach,  also  contains  mucus,  which  is  constantly  secreted 
by  the  goblet-cells  which  are  located  between  the  columnar 
epithelial  cells.  Lactic  acid,  also  acetic  and  butyric  acid, 
are  formed  in  the  gastric  juice  as  accidental  ingredients. 

The  secretions  from  the  fundus  and  pyloric  glands  differ: 
that  of  the  fundus  glands  contains  pepsin  and  hydrochloric 
acid  and  has  an  acid  reaction;  that  of  the  pyloric  glands 
has  a  neutral  or  alkaline  reaction,  contains  no  hydrochloric 
acid,  and  a  small  amount  of  pepsin  only,  consequently  it 
has  a  smaller  digestive  property  than  the  secretion  from 
the  fundus  glands. 

Natural  gastric  juice  is  obtained  by  means  of  agastric 
fistula. 

Artificial  gastric  juice  is  formed  by  adding  a  quantity  of 
pepsin  or  glycerin-pepsin  extract  to  a  solution  acidulated 
with  dilute  HCl. 

The  action  of  the  gastric  juice  upon  the  food  is  chiefly 
the  conversion  of  proteids  into  peptones. 

Proteids  are  insoluble  and  non-diffusible  albuminous  or 
albuminoid  substances;  these  in  an  acid  solution  are  trans- 
formed into  acid-albumin,  and  finally,  by  the  action  of  the 
ferment  pepsin,  mio  peptones. 

.  The  chemical  change  which  takes  place  in  this  transfor- 
mation is  called  hydration;  pepsin  is  therefore  a  hydrolytic 
ferment. 

During  the  transformation  of  proteids  into  peptones  a 
series  of  intermediate  products  are  formed  which  have 
received  various  names.  According  to  Kuhne  the  albumi- 
nous or  albuminoid  substances  are  first  divided  into  hemi- 
albuminose  and  anti-albuminose\  these  are  then  converted 
into  hemi-peptone  and  anti-peptone. 

During  pancreatic  digestion  the  hemi-peptone  is  further 
separated  into  two  organic  nitrogenous  products — namely, 
leucin  and  tyrosin;  this  is  probably  due  to  a  difference  in 
the  molecular  constitution  of  the  two  peptones. 

The  physical  and  chemical  properties  of  the  peptones  are 


THE    GASTRIC   JUICE.  129 

as  follows:  Peptones  are  soluble  in  water,  are  diffusible, 
and  can  be  precipitated  from  their  solution  upon  the  addi- 
tion of  chloride  of  mercury. 

The  chemical  test  generally  used  to  determine  the  pre- 
sence of  peptone  in  a  solution  is  the  Biuret  test,  which  is 
as  follows:  to  the  suspected  solution  add  a  few  drops  of  a 
concentrated  solution  of  potassium  hydrate,  and  then  a  few 
drops  of  a  10  per  cent  solution  of  cupric  sulphate,  and  when 
heat  is  applied  a  violet  coloration  indicates  the  presence  of 
peptone. 

Peptone  has  the  same  characteristics,  whether  formed 
from  the  albuminous  or  albuminoid  iugredients  of  meats, 
vegetables,  milk,  eggs,  etc. 

During  the  process  of  stomach  digestion  almost  all  the 
ingredients  of  food  are  disintegrated,  but  only  the  albu- 
minous and  albuminoid  substances  are  actually  changed 
and  made  absorbable.  The  digestibility  of  the  various 
articles  of  food  depends  largely  upon  their  preparation. 

Meats  swell,  the  connective  tissue  is  dissolved  by  the 
gastric  juice,  and  the  muscular  fibres  are  then  gradually 
dissolved. 

The  connective  tissue  of  fried  and  broiled  meats  is  dis- 
solved more  quickly  than  that  of  boiled  meats. 

Adipose  tissue  is  attacked  by  the  gastric  juice,  the  fib- 
rous connective-tissue  network  is  dissolved,  and  the  fat- 
globules  are  set  free. 

Milk  curdles  when  introduced  into  the  stomach,  owing 
to  the  coagulation  of  the  casein  ;  this  is  gradually  liquefied 
by  the  digestive  property  of  the  gastric  juice. 

Eggs  are  most  digestible  when  soft-boiled,  which  process 
coagulates  the  albuminous  ingredients  of  the  egg  into  fine 
flakes,  which  are  easily  and  rapidly  dissolved  in  the  gastric 
juice.  But  the  long  boiling  of  eggs  coagulates  their  all)u  - 
men  into  a  hard  mass  requiring  a  loug  time  for  its  lique- 
faction by  the  gastric  juice.  The  albumen  of  raw  eggs 
9 


130     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

coagulates  in  the  stomach  into  a  semi-sohd  colloid  mass 
which  also  is  very  slowly  digested. 

Bread  contains  principally  carbohydrate  material  and 
legumin,  the  vegetable  albuminous  substance.  The  latter 
is  dissolved  by  the  gastric  juice,  and  the  carbohydrates  are 
set  free. 

Vegetables  are  also  attacked  by  the  gastric  juice  ;  their 
nitrogenous  matter  is  digested,  and  oleaginous  and  amyla- 
ceous ingredients  are  set  free. 

The  duration  of  the  stomach  digestion  varies.  It  depends 
upon  the  quality,  quantity,  and  manner  of  preparation  of 
the  food.  It  is  estimated  that  from  four  to  six  hours  are 
required  for  the  gastric  digestion  of  a  hearty  meal  com- 
posed of  various  articles  of  food. 

The  action  of  the  gastric  juice  upon  the  various  articles 
of  food  results  in  the  formation  of  a  thickish  fluid  which 
has  an  acid  reaction  and  odor.  It  is  called  the  chyme. 
This  consists  of  water,  gastric  juice,  together  with  dissolved 
sugar,  dextrin,  acid-albumin,  peptone,  drops  of  liberated 
fat,  and  softened  masses  of  undigested  food.  It  is  essential 
that  with  the  meals,  or  shortly  after,  a  certain  quantity  of 
liquid  be  taken,  which  serves  to  give  to  the  stomach  con- 
tents a  certain  fluidity  which  is  necessary  for  the  absorp- 
tion of  digested  materials.  The  quantity  of  liquid  required 
for  this  purpose  is  best  regulated  by  the  thirst  which  the 
individual  has  when  taking  solid  foods. 

In  many  gastric  disorders  gases  develop  in  the  stomach 
as  the  result  of  an  undue  fermentation  or  decomposition  of 
foods.  Normally  the  gastric  juice,  owing  to  the  antiseptic 
properties  it  possesses,  prevents  this  decomposition,  and  it 
is  believed  by  some  that  this  is  the  most  important  property 
of  the  gastric  juice. 

The  uses  of  the  gastric  juice  may  be  enumerated  as 
follows  : 

1.  It  converts  proteids  into  peptones. 

2.  It  softens  and  disintegrates  the  food. 


THE   GASTRIC   JUICE.  131 

3.  It  acts  as  an  antiseptic. 

The  digestion  of  the  food  in  the  stomach,  and  the  action 
of  the  gastric  juice  upon  all  foods,  are  evidently  only  pre- 
paratory for  the  intestinal  digestion. 

The  chyme  contains  many  insufficiently  digested  and  en- 
tirely undigested  materials,  "which  undergo  further  changes 
in  the  intestinal  canal. 

The  peristaltic  movements  consist  of  a  peculiar  rhythmi- 
cal contraction  of  the  muscular  fibres  of  the  walls  of  the 
stomach.  By  these  movements  the  food  becomes  thor- 
oughly mixed  with  the  gastric  juice,  and  the  chyme  is  con- 
veyed into  the  duodenum  through  the  pyloric  opening, 
which  opens  periodically  by  the  relaxation  of  the  circular 
muscular  ring  and  fold  of  mucous  membrane  which  con- 
stitute the  pyloric  valve.  The  oesophageal  or  cardiac  open- 
ing of  the  stomach  is  closed  by  the  contraction  of  its  circu- 
lar muscular  fibres  during  the  process  of  stomach  digestion. 

The  nervous  mechanism  of  the  stomach  is  quite  compli- 
cated. The  motions  of  the  stomach  are  produced  by  the 
activity  of  the  automatic  gangha  and  plexuses  which  are 
contained  in  the  walls  of  the  stomach  and  which  com- 
municate with  the  vagi  and  sympathetic  nerves.  Experi- 
ments have  shown  that  such  automatic  gangha  control  the 
contraction  and  relaxation  of  the  fibres  of  the  openings  of 
the  stomach,  and  that  other  ganglia  control  the  peristaltic 
motions  of  the  muscular  walls.  Experiments  have  demon- 
strated that  these  centres  or  gangha  probably  communicate 
through  the  pneumogastric  nerves  with  nerve-centres  in 
the  brain.  This  explains  the  reflex  influence  of  mental 
emotions  upon  the  digestion. 

The  secretion  of  the  gastric  juice  is  generally  excited  by 
the  introduction  of  food  into  the  stomach.  The  mucous 
membrane  becomes  turgid  and  red,  caused  by  a  dilatation  of 
the  blood-vessels.  Section  of  the  pneumogastric  nerves  at 
this  stage  causes  a  contraction  of  the  walls  of  the  blood- 
vessels and  a  cessation  of  the  secretion,  but  this  is  only 


132        LECTURES   ON   HUMAN  PHYSIOLOGY   AND   HISTOLOGY. 

temporary.  Section  of  both  the  pneumogastric  and  sym- 
pathetic nerve-branches  of  the  stomach  is  not  followed  by 
any  serious  or  permanent  effects  on  the  secretion  of  the 
gastric  juice  or  on  the  movements  of  the  stomach.  Stimu- 
lation of  these  nerves  does  not  demonstrate  any  positive 
result  as  to  their  effect  on  the  activity  of  the  stomach  and 
its  glands.  It  must  therefore  be  supposed  that  the  motor 
and  secretory  fibres  are  derived  from  the  ganglia  in  the 
v^alls  of  the  stomach.  The  motions  of  the  stomach  and 
the  secretion  of  its  glands  are  reflex  nervous  acts.  Irri- 
tation of  certain  peripheral  nerves  sometimes  produces 
an  abnormal  contraction  of  the  muscular  walls  of  the 
stomach,  resulting  in  an  expulsion  of  the  contents  through 
the  oesophagus,  pharynx,  and  mouth — an  act  which  is 
•called  vomiting. 

Vomiting  is  caused  by  a  contraction  of  the  muscular 
walls  of  the  stomach:  the  pyloric  opening  is  closed  by  the 
contraction  of  the  muscular  fibres  of  the  valve;  the  food  is 
forced  toward  the  cardia,  which  is  distended;  this  finally 
contracts  and  forces  the  contents  of  the  stomach  through 
the  cardiac  opening  into  the  oesophagus.  Vomiting  is 
excited  by  chemical  or  mechanical  irritation  of  the  sensory 
nerves  supplying  the  mucous  membrane  of  the  palate, 
tongue,  pharynx,  or  stomach.  Irritation  of  the  uterus,  of 
the  intestines,  and  of  the  peritoneum  often  causes  vomiting. 
It  is  also  caused  by  the  direct  irritation  of  a  nerve-centre 
which  is  located  in  the  medulla  oblongata  and  is  called  the 
centre  of  vomiting;  this  centre  is  located  near  the  centre  of 
respiration,  and  it  is  believed  that  it  is  for  this  reason  that 
the  feeling  of  vomiting  can  often  be  overcome  by  taking- 
deep  inspirations.  Vomiting  also  stimulates  the  respii-a- 
tory  centre,  and  emetics  are  often  given  to  eliminate  mu- 
cus, etc.,  from  the  respiratory  passages. 

Emetics  are  drugs  which  are  given  to  cause  vomiting; 
they  do  so  either  by  their  effect  on  the  central  nervous  sys- 
tem, like  apomorphia,  or  by  their  irritating  effect  on  the 


THE    GASTRIC   JUICE.  133 

mucous  membrane  of  the  stomach,  hke  cupric  sulphate  or 
tartar  emetic.  Cerebral  irritations  caused  by  sights  or 
thoughts,  or  diseases  of  the  brain,  also  produce  vomiting. 
In  post-mortems  performed  on  persons  who  have  died 
during  the  process  of  stomach  digestion,  it  has  been  found 
that  the  walls  of  the  stomach  have  been  attacked  by  the 
gastric  juice,  and  the  question  arises,  Why  does  not  the 
gastric  juice  attack  or  digest  the  walls  of  the  stomach 
during  life  ?  Various  theories  have  been  advanced  as  an 
answer  to  this  question.  Some  believe  that  the  layer  of 
mucus  which  constantly  covers  the  mucous  lining  of  the 
stomach  prevents  this;  others  think  that  the  alkalinity 
of  the  blood,  with  which  the  walls  of  the  stomach  are  so 
freely  supplied,  is  sufficient  to  neutralize  the  acidity  of  the 
gastric  juice;  but  it  is  not  improbable  that  the  epithelium 
covering  the  mucous  lining  of  the  stomach  possesses  a 
special  protecting  property  against  the  action  of  the  gastric 
juice. 


LECTURE  XTI. 
DIGESTION  {continued). 
6.  Intestinal  Digestion. 

The  contents  of  the  stomach — i.e.,  the  chyme — as  they 
pass  through  the  pyloric  opening  into  the  intestinal  canal, 
contain  many  undigested  and  insufficiently  digested  ma- 
terials, which  in  the  intestinal  canal  undergo  further 
changes  and  are  rendered  absorbable  by  the  action  of  the 
digestive  juices  which  are  poured  into  the  intestinal  canal. 
The  changes  which  the  food  materials  undergo  in  this  por- 
tion of  the  digestive  tract  are  described  as  the  intestinal 
digestion. 

The  intestinal  canal  is  about  25  feet  long  and  is  divided 
into  the  small  and  large  intestines;  this  division  indicates 
a  difference  in  the  diameter,  not  in  the  length,  of  the  two 
portions  of  the  intestinal  canal. 

The  small  intestines  are  about  20  feet  long;  they  begin 
at  the  pyloric  opening  and  are  continuous  with  the  large 
intestines.  The  small  intestines  are  again  divided  into  three 
portions,  called  respectively  the  duodenum,  the  jejunum, 
and  the  ileum. 

The  duodenum — so  called  from  the  fact  that  it  is  about 
twelve  fingers'  breadth  in  length — is  horseshoe-shaped  and 
embraces  the  head  of  the  pancreas.  It  consists  of  an 
ascending  j)ortion,  which  passes  to  the  under- surf  ace  of  the 
liver;  a  descending  j^ortion,  which  passes  in  front  of  the 
right  kidney;  and  a  transverse  portion,  which  passes  ob- 
liquely from  right  to  left  in  front  of  the  second  and  third 
lumbar  vertebrae,  where  it  becomes  continuous  with  the 
jejunum. 


IXTESTIXAL   DIGESTION.  loO 

The  jejunum  is  so  called  from  the  fact  that  it  is  generally 
found  empty  after  death;  its  length  is  about  8  feet,  or 
about  two-fifths  of  the  length  of  the  remaining  portion  of 
the  intestinal  canal.  The  convolutions  of  the  jejunum  are 
located  principally  in  the  umbilical  and  right  iliac  regions 
of  the  abdominal  cayity. 

The  ileum  is  so  called  from  its  many  convolutions,  which 
are  located  in  the  umbihcal.  hypogastric,  and  right  iliac 
regions  of  the  abdominal  cavity.  The  ileum  is  continuous 
with  the  large  intestines  in  the  right  iliac  fossa.  The 
point  of  communication  is  guarded  by  a  fold  of  mucous 
membrane  which  is  called  the  ileo-cceca!  valve. 

The  small  intestines  are  held  in  position  by  a  fold  of  the 
peritoneum  called  the  mesentery.  The  duodenum  is  more 
firmly  fixed  than  any  portion  of  the  small  intestines. 

The  walls  of  the  small  intestines  are  composed  of  four 
coats— namely,  a  serous,  a  muscular,  an  areolar,  and  a 
mucous  coat. 

The  serous  coat  is  derived  from  the  peritoneum.  It 
covers  the  entire  external  surface  of  the  intestinal  canal, 
except  at  the  border  where  the  mesentery  is  attached, 
and  at  some  points  of  the  duodenum. 

The  muscular  coat  consists  of  fibres  of  the  non-striated 
variety.  They  are  arranged  in  an  external  longitudinal 
and  an  internal  circular  layer  ;  the  latter  forms  incom- 
plete rings  around  the  intestinal  tube. 

The  areolar  coat  is  contained  between  the  muscular  and 
mucous  coats  ;  it  serves  to  support  vessels,  glands,  etc. 

The  mucous  coat  consists  of  a  layer  of  non-striated  mus- 
cular fibres  (the  muscularis  mucosce),  of  an  areolar  layer 
(the  submucosce),  and  of  a  single  layer  of  columnar  epithe- 
lial cells  resting  on  a  deUcate  basement  membrane. 

The  mucous  membrane  of  the  small  intestines  is  ar- 
ranged in  circular  folds.  They  are  called  valvulce  conni- 
ventes,  and  serve  to  provide  a  large  surface  for  secretion 
and  absorption,  and  also  to  prevent  food  from  passing  too 


136     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

quickly  through  the  intestinal  canal.  In  order  to  accom- 
plish this  these  mucous  folds  form  incomplete  circular  rings, 
which  are  arranged  transversely  to  the  long  axis  of  the 
intestinal  tube.  They  do  not  unfold  on  distension  of  the 
intestines. 

From  the  mucous  membrane  of  the  small  intestines  are 
projected  minute,  cone-like  elevations  which  give  to  it  a 
velvety  appearance.  These  delicate  projections  are  called 
villi.  They  are  organs  intended  for  the  absorption  of  the 
saponified  oils  and  fats. 

A  microscopical  examination  of  the  mucous  membrane 
of  the  small  intestines  shows  that  between  the  villi  there 
are  minute  openings,  which  are  the  orifices  of  the  secreting 
glands  of  the  small  intestines. 

The  intestinal  juice  is  secreted  by  two  sets  of  glands — 
namely,  the  simple  follicles  or  crypts  of  LieberkuJm  and  the 
duodenal  or  Brunner^s  glands. 

The  simple  follicles  or  crypts  of  Lieberkilhn  are  distri- 
buted throughout  the  whole  intestinal  canal.  They  are 
simple,  finger-like  depressions  of  the  epithelial  lining  of 
the  intestines,  and  consist  of  abasement  membrane  covered 
with  a  single  layer  of  cylindrical  secreting  epithelial  cells 
which  have  a  glandular  protoplasm  and  large,  clear,  oval 
nuclei.  Between  these  cells  are  scattered  so-called  goblet- 
cells. 

The  duodenal  or  B runner'' s  glands  are  of  the  branching 
tubular  variety.  They  consist  of  a  number  of  convoluted 
tubules,  which  open  into  one  common  duct.  The  structure 
of  these  glands  is  similar  to  that  of  the  pyloric  glands. 

In  the  areolar  coat  of  the  small  intestines  are  small,  oval 
bodies  composed  of  adenoid  or  lymphoid  tissue.  They  are 
called  solitary  glands.  They  sometimes  form  slight  oval 
elevations  of  the  mucous  membrane,  which  are  covered  with 
numerous  villi  and  surrounded  by  openings  of  the  secreting 
glands.  These  are  most  abundant  in  the  ileum  near  the 
ileo-csecal  valve.     In  these  regions  there  are  often  found 


INTESTINAL   DIGESTION.  137 

collections  of  from  20  to  30  such  solitary  glands  in  one 
mass  ;  these  are  called  agminate  glands  or  Peyer^s  patches. 

The  lumen  of  the  small  intestines  diminishes  gradually 
from  its  beginning  to  its  termination. 

The  large  intestines  are  about  5  to  6  feet  long.  They  be- 
gin at  the  termination  of  the  small  intestines  in  the  right 
iliac  fossa  and  terminate  at  the  anus.  The  large  intestines 
are  also  divided  into  three  portions — namely,  the  caBcum, 
the  colon,  and  the  rectum. 

The  caecum,  or  caput  ccecum  coli,  which  means  the  blind 
head  of  the  colon,  is  a  pouch-like  expansion  which  is 
situated  in  the  right  iliac  fossa  and  communicates  with 
the  small  intestines,  the  opening  of  communication  being 
guarded  by  a  reduplication  of  mucous  membrane,  called 
the  ileo-ccecal  valve.  From  the  posterior  wall  of  the  caecum 
is  projected  an  appendix,  called  the  appendix  vermiformis. 
This  is  from  3  to  5  inches  long,  with  a  diameter  of  about 
that  of  a  goose-quill.  It  communicates  with  the  caecum 
and  is  lined  with  mucous  membrane  continuous  with  that 
of  the  caecum.  In  the  caecum  and  the  appendix  are  found 
solitary  and  agminate  glands. 

The  colon  begins  in  the  right  iliac  fossa,  and  passes  from 
here  as  the  ascending  portion  up  to  the  under-surf  ace  of  the 
liver,  where  it  forms  the  ?iep>atic  flexure ;  then  it  passes  as 
the  transverse  colon  to  the  spleen,  forms  here  the  splenic 
flexure,  and  then  passes  down  into  the  left  ihac  fossa, 
where  it  forms  the  sigmoid  flexure,  which  is  continuous 
with  the  rectum. 

The  rectum  is  the  last  portion.  It  is  about  6  inches  long 
and  terminates  at  the  anus. 

The  walls  of  the  large  intestines  consist  of  the  same  four 
coats  as  the  walls  of  the  small  intestines. 

The  longitudinal  fibres  of  the  large  intestines  are  ar- 
ranged in  three  flat  bands  and  give  to  the  intestinal  tube 
a  sacculated  appearance.  The  circular  fibres  form  a  uni- 
form layer  and  are  most  abundant  at  the  lower  portion  of 


138      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

the  rectum,  where  they  form  the  internal  sphincter  of  the 
anus.  The  mucous  membrane  of  the  large  intestines  is 
also  thrown  into  circular  folds,  particularly  at  the  sac 
culations.  The  glands  of  the  large  intestines  are  solitary 
and  agminate  glands  and  simple  follicles  ;  the  latter  differ 
from  those  of  the  small  intestines  in  that  they  are  larger 
and  have  a  greater  number  of  goblet  cells  scattered  in  the 
epithelial  lining.  The  secretion  of  the  follicles  of  the  large 
intestines  is  for  this  reason  more  tenacious  and  slimy  than 
that  of  the  follicles  of  the  small  intestines.  The  mucous 
membrane  of  the  large  intestines  is  smooth  ;  no  villi  are 
projected  from  its  surface.  The  blood-supply  to  the  small 
and  the  large  intestines  is  by  branches  from  the  superior 
and  inferior  mesenteric  arteries.  The  venous  blood  is  con- 
veyed into  the  portal  vein  through  the  superior  and  inferior 
mesenteric  veins. 

The  nerve-supply  to  the  intestines  is  from  the  superior 
mesenteric  plexus  of  the  sympathetic  nerve,  branches  of 
which  enter  the  walls  of  the  intestines  together  with  the 
vessels,  and  communicate  with  nerve-plexuses  which  are 
situated  in  the  muscular  coat.  They  are  called  Auerbacli's 
plexuses,  and  these  again  communicate  with  Meissner^s 
plexuses,  which  are  situated  between  the  muscular  and 
the  mucous  coats  ;  from  these  filaments  are  distributed  to 
the  glands,  mucous  membrane,  etc. 

The  secretion  of  the  glands  of  the  intestinal  canal  is 
called  the  intestinal  juice,  or  succus  entericus.  This  may 
be  obtained  by  an  intestinal  fistula. 

The  intestinal  juice  is  a  yellowish,  alkaline  fluid  which 
has  a  specific  gravity  of  1011  and  contains  about  2  to  2| 
per  cent  of  solids.  It  is  composed  of  water,  alkaline  salts, 
and  albuminous  matter — namely,  mucin  and  ferment 
substances  of  an  unknown  nature. 

Intestinal  juice  must  be  considered  mainly  as  the  secre- 
tion of  Lieberkiihn's  follicles.  The  nature  of  the  secretion 
if  Brunner^s  glands  is  not  exactly  known. 


INTESTINAL   DIGESTION.  139 

The  uses  of  the  intestinal  juice  may  be  enumerated  as 
follows: 

1.  It  converts  proteids  into  peptones.  This  action  is  due 
to  a  ferment  which  acts  only  in  an  alkaline  medium. 

2.  It  changes  starch  into  sugar,  and  maltose  into  glucose. 
These  changes  are  also  due  to  a  ferment.  The  diastatic 
property  of  intestinal  juice  is  not  as  pronounced  as  that  of 
the  saliva  or  pancreatic  juice. 

3.  It  changes  cane  sugar  and  lactose  into  levulose  or 
inverted  sugar.  This  transformation  is  caused  by  the 
presence  of  a  ferment  called  invertin. 

Besides  the  intestinal  juice  there  are  two  other  digestive 
juices  w^hich  have  a  part  in  the  process  of  intestinal  diges- 
tion; these  are  ih.Q  pancreatic  juice  and  the  hile,  which  are 
secreted  by  the  accessory  glands — viz.,  by  the  pancreas  and 
the  liver — and  are  poured  into  the  small  intestines. 

The  pancreas,  or  abdominal  salivary  gland,  is  situated  in 
the  abdominal  cavity  in  the  posterior  part  of  the  epigastric 
region  and  in  relation  with  the  lower  and  posterior  portion 
of  the  stomach.  The  gland  is  hammer-shaped  and  has  a 
head,  a  body,  and  a  tail.  The  head,  or  right  extremity, 
bends  downward  and  is  embraced  by  the  duodenum;  the 
body  passes  across  the  lower  border  of  the  stomach  to  the 
left;  and  the  tail,  or  tapered  end  of  the  gland,  extends  to 
the  spleen.  The  head  is  sometimes  detached  and  forms  a 
separate  part,  called  the  lesser  piancreas. 

The  pancreas  is  from  6  to  8  inches  long  and  weighs  from 
3  to  5  ounces. 

The  structure  of  the  pancreas  is  similar  to  that  of  the 
salivary  glands.  It  is,  like  these,  a  gland  of  the  compound 
tubular  or  compound  racemose  variety.  The  gland  is 
pierced  by  a  central  duct,  called  Wirsung\s  duct,  which 
passes  from  the  tail  portion  to  the  head  and  opens  into  the 
duodenum  about  10  centimetres  from  the  pyloric  opening. 

The  gland  consists  of  lobules,  each  of  which  has  a  duct 
(the  lobular  duct)  which  opens  into  the  main  duct  of  the 
gland.     This  divides  into  minor  tubules,  called  the  intra- 


140       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

lobular  ducts,  and  each  of  these  terminates  in  a  pouch-Hke 
expansion,  the  alveolus. 

These  various  portions  of  the  gland  are  composed  of  a 
deHcate  basement  membrane  and  are  hned  with  epithehal 
cells.  The  ducts,  ductules,  and  tubular  portions  of  the 
gland  are  lined  with  columnar  epithelium. 

The  alveoli  are  lined  with  a  single  layer  of  columnar 
secreting  cells.  The  body  of  these  cells  shows  two  distinct 
zones — namely,  a  granular  zone  toward  the  lumen  of  the 
alveolus,  and  a  clear,  homogeneous  zone  which  is  directed 
toward  the  basement  membrane  of  the  alveolus.  At  the 
junction  of  these  two  zones  is  situated  a  large,  oval  nu- 
cleus. Heidenhain  observed  that  during  the  first  period — 
that  is,  from  the  sixth  to  the  tenth  hour — of  intestinal  di- 
gestion, when  the  secretion  of  the  pancreas  is  most  active, 
the  granular  inner  zone  of  the  epithelial  cells  lining  the 
alveoli  decreases,  and  that  after  that  period  it  again  gradu- 
ally increases.  It  is  believed  that  the  outer,  homogeneous 
zone  takes  materials  from  the  blood,  which  are  transformed 
into  the  granular  protoplasm  of  the  inner  zone  w^hich 
forms  the  ingredients  of  the  secretion  of  the  gland. 

The  various  structures  of  the  pancreas  are  held  together 
by  areolar  tissue,  which  also  supports  the  vessels  and 
nerves  of  the  gland. 

The  blood-supply  of  the  pancreas  is  from  branches  of  the 
splenic,  hepatic,  and  superior  mesenteric  arteries.  The 
veins  open  into  the  portal  vein. 

The  nerve-supply  is  from  fibres  of  the  splenic  plexus  of 
the  sympathetic  nerve.  The  exact  distribution  and  termi- 
nation of  the  nerve-filaments  in  the  gland  is  unknown. 

The  pancreatic  juice  is  obtained  by  means  of  a  fistula. 
It  is  a  colorless  and  odorless  liquid,  having  a  saline  taste,  a 
strong  alkaline  reaction,  and  a  specific  gravity  of  1010  to 
1015.  It  contains  from  6  to  10  per  cent  solid  ingredients, 
of  which  nine-tenths  are  organic  and  one-tenth  inorganic 
material.     The  large   amount  of  albuminous  ingredients 


INTESTINAL  DIGESTION.  141 

causes  the  paDcreatic  juice  to  coagulate  into  a  jelly  like 
mass  when  heated. 

The  composition  of  the  pancreatic  juice  is  as  follows  : 

Water 911. 

Organic  matter 81. 

Namely,  serum-albumin  and  ferments. 

Inorganic  salts 8. 

Namely,  sodium  chloride,  sodium  carbon- 
ate,   magnesium    phosphate,    calcium 

phosphate 

The  ferments  of  the  pancreatic  juice  are  trypsin,  amy- 
lopsin,  and  steapsin. 

Pancreatic  juice,  in  the  presence  of  the  various  bacteria 
existing  in  the  intestinal  canal,  easily  decomposes  owing 
to  its  great  percentage  of  albuminous  material.  The  juice 
then  assumes  a  brownish  color  and  a  fetid  odor,  which  is 
due  to  the  formation  of  fetid  gases  and  to  the  production 
of  two  decomposition  products  of  albuminous  substances. 
These  are  called  indol  and  skatol. 

The  actions  and  properties  of  pancreatic  juice  are  as 
follows  : 

1.  Starch  is  transformed  into  sugar.  This  diastatic  ac- 
tion is  due  to  the  ferment  called  amylopsin. 

2.  Proteids  are  converted  into  peptones.  The  proteoly- 
tic ferment  causing  this  change  is  called  trypsin.  It  differs 
from  pepsin  in  that  it  acts  only  in  an  alkaline  medium. 
During  the  pancreatic  digestion  the  proteids  are  first  trans- 
formed into  alkali  albumin,  which  is  separated  into  hemi- 
and  anti  albumin,  and  this  finally  is  converted  into  anti- 
and  hemi-peptone.  During  the  pancreatic  digestion  two 
organic  nitrogenous  substances,  called  leucin  and  tyrosin, 
are  formed  as  products  of  the  continued  action  of  panci'e- 
atic  juice  on  hemi-peptone. 

3.  Fats  and  oils  are  separated  into  glycerin  and  fatty 
acids.  Thin  the  latter  with  the  alkaline  salts  present, 
saponify,   and  with   water  form  an  absorbable  emulsion. 


142      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  division  of  the  fats  is  caused  by  the  presence  of  a  fer- 
ment called  steapsin. 

The  ferments  of  the  pancreatic  juice  are  also  called 
enzymes.  They  do  not  pre- exist  in  the  blood,  but  are  found 
in  the  secreting  cells  from  materials  taken  from  the  blood. 
The  granular  protoplasm  of  the  inner  zone  of  the  secreting 
cells  lining  the  alveoli  of  the  pancreas  is  called  zymogen; 
as  such,  it  possesses  none  of  the  characteristic  properties 
of  the  enzymes,  but  it  is  transformed  into  these  during 
secretion. 

Pancreatic  juice  is  not  secreted  continuously,  but  only 
when  food  is  taken.  The  secretion  gradually  increases 
during  the  first  ten  hours,  when  it  begins  to  decrease 
again. 

The  quantity  of  pancreatic  juice  secreted  in  twenty-four 
hours  has  not  been  exactly  determined,  but  it  is  certainly 
much  more  scanty  than  that  of  the  other  digestive  juices. 

The  pancreatic  secretion  is  a  reflex  nervous  act.  Ordi- 
narily the  introduction  of  food  is  the  stimulus.  During 
secretion  the  gland  becomes  red  and  enlarged,  owing  to  a 
dilatation  of  the  blood-vessels. 

Extirpation  of  the  pancreas  causes  diabetes  mellitus. 


LEOTUEE  XTII. 

THE  DIGESTION  {continued). 
The  Bile. 

The  third  digestive  juice  which  takes  part  in  the  intesti- 
nal digestion  is  the  hile;  it  is  secreted  by  the  hver,  and  is 
conveyed  into  the  gall-bladder  and  thence  into  the  duo- 
denal portion  of  the  small  intestines. 

The  liver  is  the  largest  secreting  gland  in  the  body;  it 
weighs  about  1,600  grammes  and  is  situated  in  the  abdomi- 
nal cavity,  occupying  the  left  hypochondriac  and  part  of 
the  epigastric  regions.  The  upper,  convex  surface  of  the 
liver  is  in  relation  with  the  under-surface  of  the  diaphragm; 
the  lower,  concave  surface,  with  the  stomach,  duodenum, 
and  the  hepatic  flexure  of  the  colon;  and  its  anterior,  late- 
ral, and  posterior  surfaces,  with  the  parietes  of  the  ab- 
dominal cavity. 

The  liver  is  held  in  position  by  five  ligaments;  these  are, 
the  longitudinal,  the  coronary,  the  two  lateral,  and  the 
round  hgaments.  The  first  four  mentioned  ligaments  are 
folds  of  peritoneum;  the  round  ligament  is  the  obhterated 
umbihcal  vein. 

The  hver  is  made  up  of  five  lobes;  these  are  called  the 
right  lobe,  the  left  lobe,  the  lohus  quadratus,  the  lobus  cau- 
datus,  and  the  lobus  Spigelii. 

The  five  lobes  of  the  hver  are  separated  by  five  fis- 
sures: namely,  the  transverse  fissure,  the  longitudinal  fis- 
sure, the  fissure  for  the  gall-bladder,  the  fissure  for  the 
ductus  venosus,  and  iYiQ  fissure  for  the  inferior  vena  cava. 

The  liver  is  covered  with  a  layer  of  peritoneum,  beneath 
which  is  a  layer  of  fibrous  tissue,  the  visceral  layer  of 


144      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

which  sends  nuraerous  prolongations  into  the  substance  of 
the  liver,  forming  numerous  small  compartments  which 
are  filled  with  liver- tissue  and  form  the  lobules.  The 
fibrous  covering  and  the  compartments  formed  by  its  pro- 
longations are  called  Glissons  capsule;  a  reflexion  of  this 
forms  a  sheath  for  the  structures  entering  and  leaving  the 
liver  at  its  transverse  fissure. 

A  liver  lobule  is  oblong,  about  one-twelfth  of  an  inch  in 
diameter,  and  is  made  up  of  the  following  structures: 

1.  The  hepatic  cells. 

2.  A  capillary  plexus  of  the  portal  vein. 

3.  A  capillary  plexus  of  the  hepatic  artery. 

4.  The  bile-channels,  which  are  formed  by  adjacent  sides 
of  the  hepatic  cells. 

These  structures  are  held  together  and  the  whole  lobule 
is  surrounded  by  a  delicate  fibrous  tissue. 

The  hepatic  cells  are  ^-^Vo  to  ;g-^  of  an  inch  in  diameter; 
they  are  polygonal  and  have  one  or  two  nuclei;  their  cell- 
body  contains  a  granular  protoplasm,  albumin,  oil-globules, 
glycogen,  bile  pigments,  and  salts.  They  are  secreting 
cells  and  secrete  from  the  blood  the  materials  for  the  bile; 
they  also  possess  the  property  of  producing  glycogen. 

The  capillary  plexus  of  the  portal  vein  contains  the 
blood  from  which  the  hepatic  cells  principally  derive  the 
materials  for  their  secretion.  The  portal  vein  is  a  short 
trunk  which  is  formed  by  the  union  of  the  superior  and 
inferior  mesenteric  and  splenic  and  gastric  veins.  The 
portal  vein  enters  the  liver  at  its  transverse  fissure  and 
there  gives  off  separate  branches  to  the  lobes;  these  ramify 
and  give  off  branches  which  pass  between  and  around  the 
lobules — these  are  called  the  interlobular  veins;  from  these 
again  branches  are  given  off  which  pass  into  the  lobule 
and  form  in  it  an  intralobular  plexus;  in  the  middle  of  the 
lobule  these  capillaries  open  into  a  larger  vein,  which  is 
called  the  intralobular  vein;  this  passes  out  of  the  lobule 
and  opens  into  a  small  vein  at  the  base  of  the  lobule,  called 
the  sublobular  vein,  from  which  the  hepatic  veins  spring. 


THE  BILE.  145 

The  capillary  plexus  of  the  hepatic  artery  supphes  the 
nutrition  for  the  structures  of  the  lobules.  The  hepatic  ar- 
tery enters  the  liver  at  the  transverse  fissure  together  with 
the  portal  vein;  in  its  course  it  gives  off  branches  to  the 
lobes  and  lobules;  in  the  latter  the  artery  breaks  up  into  a 
capillary  plexus,  which  finally,  together  with  the  capillary 
plexus  of  the  portal  vein,  terminates  in  the  sublobular 
vein. 

The  hile-channels  are  the  beginning  of  the  hepatic  duct, 
by  which  the  secretion  of  the  fiver  is  conveyed  directly  or 
indirectly  to  the  intestinal  canal.  The  hile-channels  begin 
as  minute  spaces  between  the  hepatic  ceUs;  the  walls  of 
the  bile -channels  are  formed  only  by  the  adjacent  sides  of 
the  hepatic  cells.  These  minute  channels  radiate  toward 
the  periphery  of  the  lobule,  where  they  communicate  with 
delicate  vessels,  the  interlobular  bile-ducts;  these  ramify 
between  the  lobules  and  gradually  increase  in  diameter, 
until  finally  a  main  duct  emerges  from  the  structure  of  the 
left  and  one  from  that  of  the  right  portion  of  the  liver. 
These  right  and  left  hepatic  ducts  then  unite  and  form  the 
common  hepatic  duct.  The  walls  of  these  ducts  are  com- 
posed of  fibrous  tissue  and  contain  non-striated  muscular 
fibres.  The  ducts  are  fined  with  mucous  membrane,  which, 
in  the  smaller  ducts,  is  covered  with  polygonal,  and  in  the 
larger  ducts  with  cylindrical,  epithelial  ceUs.  The  portal 
vein,  the  hepatic  artery,  and  the  hepatic  ducts  pursue  the 
same  course  through  the  liver;  they  are  contained  in  a 
fibrous  sheath,  which  is  called  the  portal  canal,  formed  by 
a  reflexion  of  the  fibrous  covering  of  the  liver.  A  trans- 
verse section  of  the  portal  canal  shows  the  openings  of  a 
portal  vein,  a  hepatic  artery,  and  a  hepatic  duct,  which  are 
distinguished  by  the  characteristic  structure  of  their  waUs. 

The  blood  of  the  liver  is  conveyed  into  the  inferior  vena 
cava  by  the  three  hepatic  veins.  These  begin  at  the  capil- 
lary termination  of  the  portal  vein  and  hepatic  artery, 
pursue  independent  courses  through  the  substance  of  the 

10 


146      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

liver,  and  emerge  at  its  posterior  surface.  The  hepatic 
veins  in  their  course  are  not  found  within  the  portal  canals. 

The  liver  is  supplied  with  superficial  and  deep  lympha- 
tics. 

The  superficial  lymphatics  form  a  delicate  network  on 
the  surface  of  the  organ. 

The  deep  lymphatics  begin  in  the  lobules;  outside  of 
these,  lymph-ducts  and  vessels  form,  which  ramify  between 
the  lobules  and  lobes,  and  in  their  course  accompany  the 
portal  vein,  hepatic  artery,  hepatic  duct,  and  hepatic  veins, 
and  finally  leave  the  organ  with  these. 

The  nerves  of  the  liver  are  from  the  hepatic  plexus, 
which  is  composed  of  fibres  of  the  vagus  and  of  the  sympa- 
thetic. The  nerves  accompany,  in  their  course  through  the 
liver,  the  ramifications  of  the  hepatic  artery.  The  nerves 
of  the  liver  contain  vasomotor  and  secretory  fibres. 

The  functions  of  the  liver  are: 

1.  The  glycogenetic  function — namely,  the  property  of 
producing  glycogen.  This  function  I  will  describe  in  detail 
when  treating  the  subject  of  the  elaboration  and  assimila- 
tion of  the  absorbed  food  materials. 

2.  The  secretion  of  the  bile. 

Before  describing  the  mode  of  the  secretion  of  bile  I  will 
describe  its  physical  properties  and  its  chemical  composi- 
tion. 

The  physical  properties  of  bile  may  be  said  to  be  as  fol- 
lows: Bile  is  a  viscid,  transparent  fiuid  which  has  a  yel- 
low, sometimes  a  brown  or  dark-green  color;  its  reaction 
is  neutral;  its  specific  gravity  is  1020  to  1030.  Bile  is  best 
obtained  by  means  of  a  hepatic  fistula,  as  that  obtained 
from  the  gall-bladder  is  darker  and  more  viscid. 

The  chemical  composition  of  bile  is  as  follows:  water, 
823  parts;  solids,  177  parts. 

The  solid  ingredients  of  the  bile  are: 

1.  The  bile-salts  and  the  bile-pigments. 

2.  Fat. 


THE   BILE.  147 

3.  Cholesterin. 

4.  Mucus. 

5.  Inorganic  salts  and  minerals. 

The  specific  ingredients  of  the  bile  are  the  bile-salts  and 
the  bile-pigments.  These  do  not  pre-exist  as  such  in  the 
blood  of  the  liver,  but  are  formed  from  materials  taken 
from  the  blood  bj  the  hepatic  cells,  and  it  is  believed  that 
these  materials  are  furnished  by  the  red  blood- corpuscles, 
a  great  number  of  which  undergo  destruction  in  the  liver; 
this  is  demonstrated  by  the  decrease  in  the  number  of  red 
blood-corpuscles  in  the  blood  of  the  hepatic  veins,  as  com- 
pared with  their  number  in  the  portal  vein  and  hepatic 
artery.  In  the  latter  vessels  the  proportion  of  the  white 
and  red  blood-corpuscles  is  1  white  to  740  red,  while  in  the 
hepatic  veins  the  proportion  is  1  white  to  170  red. 

The  bile-salts  are  the  sodium  glycocholate  and  sodium 
taurocholate.  They  are  formed  by  the  liver-cells  from  the 
albuminous  material  of  the  destroyed  red  blood-corpuscles; 
their  formation  is  a  chemical  process,  consisting  in  a  divid- 
ing of  the  albuminous  material  into  taurin,  glycin,  and 
cholic  acid;  these  unite  and  form  taurocholic  and  glyco- 
cholic  acids,  which  unite  with  sodium  to  form  the  bile- 
salts  named. 

The  bile-salts  constitute  about  9  per  cent  of  the  soUd  in- 
gredients of  the  bile.  In  the  human  bile  the  sodium  glyco- 
cholate preponderates.  The  difference  in  the  two  salts  is 
that  the  sodium  taurocholate  contains  sulphur. 

The  bile-salts  are  soluble  in  water,  alcohol,  and  alkaline 
fluids,  and  can  be  precipitated  from  their  solution  in  the 
form  of  colorless,  needle-like  crystals. 

The  chemical  test  generally  employed  to  determine  the 
presence  of  bile-salts  is  that  prescribed  by  Petterikofer.  It 
is  performed  as  follows:  To  the  suspected  solution  are  first 
added  a  few  drops  of  a  strong  solution  of  sulphuric  acid, 
and  this  is  followed  by  the  addition  of  a  small  quantity  of 
a  10  per  cent  solution  of  cane-sugar;  the  result  is  the  forma- 


]48       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

tioii  of  a  substance  called  furfurol,  which  in  the  presence 
of  bile-salts  assumes  a  bright-red  or  purple  color,  and  it  is 
this  coloration  of  the  suspected  solution  which  indicates 
the  presence  of  bile-salts. 

The  hilepigments  are  bilirubin  and  hiliverdin.  They 
are  formed  by  the  hepatic  cells  from  the  haemoglobin  of 
the  destroyed  red  blood-corpuscles. 

It  is  believed  that  the  bile-pigments  are  non-essential 
products  which  form  during  the  formation  of  bile-salts. 
The  bile- pigments  do  not  partake  in  the  action  of  the  bile. 

Bilirubin  is  obtained  from  the  bile  in  the  form  of  yellow, 
rectangular  crystals  which  are  soluble  in  water,  alcohol, 
and  chloroform. 

Biliverdin  is  the  green  coloring  matter  of  the  bile;  it  is 
most  abundant  in  the  bile  of  the  herbivora;  it  is  formed 
from  bilirubin  as  the  result  of  oxidation. 

Biliverdin  is  obtained  from  the  bile  in  the  form  of  an 
amorphous  powder  which  is  soluble  in  alcohol  and  in  a 
solution  of  bile- salts,  but  insoluble  in  water. 

In  bile  which  has  been  retained  for  a  time  m  the  gall- 
bladder a  third  coloring  matter  is  found,  which  is  dark  and 
is  called  biliprasin;  it  is  formed  by  an  oxidation  of  the 
biliverdin. 

The  chemical  test  generally  employed  for  bile-pigments 
is  that  of  Gmeliii.  Add  to  the  suspected  solution  first  a 
few  drops  of  nitric  and  then  a  few  drops  of  nitrous  acid; 
if  bile-pigments  are  present  a  number  of  colored  rings  ap- 
pear, in  the  following  order:  green,  blue,  violet,  red,  and 
indigo;  they  indicate  the  degree  of  oxidation  of  the  color- 
ing matters. 

Normally  the  bile-pigments  are  formed  only  in  the  liver; 
but  in  certain  conditions — for  instance,  after  the  intravas- 
cular injection  of  a  solution  of  bile-salts,  after  long  chloro- 
form narcosis,  in  fact  in  most  pathological  or  other  condi- 
tions in  which  a  destruction  of  red  blood-corpuscles  takes 
place  in  the  circulating  blood — bile-pigments  are  formed  in 
the  blood. 


THE    BILE.  149 

In  conditions  where  the  flow  of  the  bile  from  the  hver  is 
interfered  with,  owing  to  an  obstruction  of  the  bile  ducts, 
bile  is  absorbed  by  the  blood.  Whenever  bile  pigments 
exist  in  the  blood  their  presence  is  indicated  by  a  yellowish 
discoloration  of  the  skin  and  of  the  sclerotic  of  the  eye — a 
condition  which  is  called  icterus  ov  jaundice.  If  the  icterus 
is  due  to  the  formation  of  bile-pigments  in  the  blood  it  is 
called  hcematogenetic  icterus;  if  the  icterus  is  due  to  the 
absorption  of  bile-pigments  into  the  blood  it  is  called  hejja- 
togenetic  icterus. 

The  other  ingredients  of  the  bile — namely,  the  choles- 
terin,  lecithin,  palmitiyi,  olein,  and  stearin,  traces  of  urea, 
and  a  diastatic  ferment  of  an  unknown  nature — pre-exist 
in  the  blood  from  which  the  bile  is  secreted.  The  inor- 
ganic ingredients  of  the  bile — namely,  the  water  and  salts, 
principally  sodium  and  potassium  chloride,  and  the  phos- 
phates of  calcium  and  magnesium — are  also  taken  as  such 
from  the  blood.  The  mucus  contained  in  the  bile  is 
secreted  by  the  epithelial  cells  of  the  mucous  membrane 
lining  the  bile-ducts  and  gall-bladder. 

Iron,  which  forms  a  constant  ingredient  of  bile,  is  de- 
rived from  the  HO  of  the  destroyed  red  blood- corpuscles  in 
the  liver.  Bile  also  contains  a  small  amount  of  gas,  princi- 
pally oxygen,  nitrogen,  and  carbon  dioxide;  these  are  de- 
rived from  the  blood,  into  which  they  have  been  absorbed 
from  the  intestinal  canal. 

The  question  arises:  From  which  kind  of  blood  do  the 
hepatic  cells  take  the  materials  for  their  secretion,  from 
that  of  the  portal  vein  or  from  that  of  the  hepatic  artery  ? — 
both  vessels  forming  a  capillary  plexus  in  the  liver  lobule. 

Observations  and  experiments  tend  to  show  that  it  is 
principally  the  blood  of  the  portal  vein  from  which  the 
cells  derive  their  materials.  The  distribution  of  the 
branches  of  the  hepatic  artery  indicates  that  this  vessel  is 
intended  mainly  for  the  nutrition  of  the  structures  of  the 
liver. 

If  the  hepatic  artery  is  ligated  the  secretion  of  bile  does 


150      LECTURES   ON   HUMAN   PHYSIOLOGy   AND    HISTOLOGY. 

not  cease,  but  gangrene  of  the  liver  occurs  owing  to  insuf- 
ficient nutrition  of  its  structures. 

Ligation  of  the  portal  vein  causes  death,  through  venous 
congestion  of  the  abdominal  viscera,  so  quickly  that  no  ob- 
servations as  regards  the  effects  of  the  ligation  of  that  ves- 
sel on  the  hepatic  secretion  can  be  made.  If  through  a 
pathological  condition  the  portal  circulation  in  a  part  of 
the  liver  is  obliterated,  a  collateral  circulation  will  soon  be 
established. 

If  a  branch  of  the  portal  vein  supplying  a  lobe  of  the 
liver  is  ligated,  the  bile  secretion  in  that  lobe  will  be  di- 
minished, but  not  cease  entirely,  which  fact  tends  to  show 
that  the  hepatic  artery  also  furnishes  materials  for  the  se- 
cretion of  the  bile. 

Bile  is  secreted  continually ;  during  the  period  of  intesti- 
nal digestion  the  bile  is  poured  directly  into  the  duodenum; 
during  the  interval  the  bile  is  stored  in  the  gall-bladder. 

The  gall  bladder  is  a  membranous  sac  holding  from  6  to 
8  drachms;  it  is  situated  at  the  nnder-surface  of  the  right 
lobe  of  the  liver.  Its  duct,  called  the  cystic,  joins  the  com- 
mon hepatic  duct  and  forms  one  duct,  which  is  called  the 
ductus  communis  choledochns;  this  is  about  the  size  of  a 
goose-quill,  and  opens  into  the  posterior  wall  of  the  duode- 
num together  with  the  pancreatic  duct.  The  gall-bladder 
and  its  duct  are  lined  with  mucous  membrane  which  is 
continuous  with  that  lining  the  hepatic  duct.  The  walls 
of  the  gall-bladder  contain  non -striated  muscular  fibres, 
which  are  arranged  transversely  and  longitudinally;  the 
introduction  of  food  into  the  intestinal  canal  by  reflex  ac- 
tion causes  a  contraction  of  these  muscular  fibres,  by  which 
the  bile  stored  in  the  gall-bladder  is  forced  through  the 
cystic  duct  and  the  ductus  communis  choledochns  into  the 
duodenum. 

During  the  interval  of  digestion  the  opening  of  the  duc- 
tus communis  choledochns  into  the  duodenum  is  closed, 
and,  the  flow  of  the  bile  not  being  sufficient  to  force  an 
opening,  the  bile  is  forced  back  into  the  gall-bladder. 


THE   BILE.  151 

The  quantity  of  bile  secreted  in  twenty-four  hours  by  the 
healthy  human  adult  has  been  estimated  to  be  from  700  to 
900  grammes. 

The  secretion  of  bile  is  influenced  by  many  conditions, 
which  may  be  enumerated  as  follows: 

1.  The  quality  of  food  influences  the  secretion  of  the 
bile;  it  has  been  observed  that  it  is  increased  when  food 
rich  in  albuminous  material  is  taken. 

2.  The  blood-supply  to  the  liver  influences  its  secretion; 
it  is  for  this  reason  that  during  the  process  of  digestion, 
when  the  organs  concerned  in  the  process  are  congested, 
the  secretion  of  bile  is  more  abundant. 

3.  Nerves  influence  the  secretion  of  bile;  the  termination 
of  the  nerve-flbres  in  the  liver  is  not  exactly  known.  Stim- 
ulation of  the  right  pneumogastric  below  the  diaphragm 
has  no  effect  on  the  bile-secretion;  section  of  the  nerve  at 
the  same  point  also  does  not  influence  the  activity  of  the 
liver;  section  or  stimulation  of  the  right  pneumogastric 
above  the  diaphragm  decreases  or  increases  the  flow  of 
bile,  but  only  as  the  result  of  the  influence  of  such  section 
or  stimulation  on  the  respiratory  movements.  Stimulation 
of  the* liver  by  electrical  currents  increases  the  flow  of  bile, 
but  does  so  only  by  causing  a  contraction  of  the  bile-ducts. 

It  may  be  said  that  all  conditions  which  increase  the 
blood-pressure  in  the  liver  also  increase  the  secretion  of 
bile,  and  vice  versa. 

The  proper  quality  of  the  bfle  depends  upon  a  normal 
activity  of  the  hepatic  cells  and  upon  a  proper  condition  of 
the  blood  and  its  ingredients. 


LECTURE  XVril. 
DIGESTION  {continued). 

TJw  Bile. 

The  actions  and  uses  of  the  bile  as  a  digestive  juice  may 
be  enumerated  as  follows  : 

1.  Bile  assists  in  the  emulsification  of  the  fats  in  the  in- 
testinal canal.  Bile  when  mixed  with  oil  forms  an  emul- 
sion. The  fats  are  divided  into  fatty  acids  and  glycerin 
by  the  action  of  pancreatic  juice  in  the  small  intestines, 
and  then  form  with  the  bile  an  emulsion  in  which  fats  are 
absorbable. 

2.  Bile  prevents  a  continuation  of  the  gastric  digestion 
in  the  small  intestines.  The  bile-salts,  as  they  come  in  con- 
tact with  the  acidulous  chyme  which  is  conveyed  into  the 
small  intestines,  are  separated  by  the  action  of  the  gastric 
juice.  The  glycocholic  acid  is  precipitated  by  the  gastric 
juice,  and  with  it  precipitates  the  pepsin.  The  albumin- 
ous and  albuminoid  ingredients  of  the  chyme  are  precipi- 
tated by  the  taurocholic  acid. 

3.  Bile  aids  in  the  absorption  of  the  fats.  Bile  is  a  soapy 
fluid  ;  it  moistens  the  mucous  membrane  of  the  small  intes- 
tines and  thus  favors  a  transfusion  of  the  emulsified  fats. 

4.  Bile  retards  putrefaction  of  the  intestinal  contents, 
although  bile  itself  undergoes  a  rapid  decomposition  when 
exposed  to  air. 

5.  Bile  stimulates  the  muscular  fibres  of  the  intestinal 
canal  and  thus  stimulates  peristalsis  and  secretion. 

6.  The  water  of  the  freely  secreted  bile  serves  to  give 
the  soft  consistence  to  the  fa?ces. 

7.  Bile  has  a  slight  diastatic  action,  owing  to  the  pre- 
sence of  a  diastatic  ferment. 


THE    BILE,  153 

The  importance  of  bile  as  a  digestive  fluid  is  well  demon- 
strated by  the  conditions  which  arise  when  the  flow  of  the 
bile  into  the  intestinal  canal  is  interfered  with.  Incom- 
plete intestinal  digestion  and  constipation  are  the  imme- 
diate results  ;  the  stools  assume  a  clay  color,  owing  to  the 
presence  of  a  great  quantity  of  unabsorbed  fat;  the  faeces 
are  dry  and  hard,  contain  many  undigested  materials,  and 
are  characterized  by  a  strong  fetid  odor.  Constipation 
is  due  to  the  want  of  the  stimulating  effect  of  the  bile  on 
the  muscular  coat  of  the  intestinal  canal. 

The  studies  and  observations  as  to  the  final  destination 
of  bile-ingredients  in  the  intestinal  canal  have  led  to  the 
following  conclusions: 

1.  The  luater  is  eliminated  to  the  greatest  extent  with  the 
fgeces. 

2.  The  bile-salts  are  reabsorbed  in  the  intestinal  canal; 
they  are  changed  during  their  absorption,  and  they  are  not 
found  as  such  in  the  blood:  therefore  it  is  believed  that 
they  serve  further  uses  in  the  economy.  Traces  of  them 
are  excreted  with  the  faeces  and  urine. 

3.  The  coloring  matters  are  to  some  extent  reabsorbed  in 
the  intestinal  canal,  but  undergo  changes  during  this  pro- 
cess ;  they  are  finally  excreted  by  the  kidneys  as  urobilin, 
the  coloring  matter  of  the  urine. 

A  portion  of  the  bile-pigments  undergo  a  process  of  re- 
duction and  are  eliminated  as  stercobilin  and  hydrobiliru- 
bin — two  coloring  matters  of  the  fceces. 

4.  The  lecithin  and  cholesterin  contained  in  the  bile  are 
eliminated  with  the  faeces. 

5.  The  inorganic  salts  are  to  the  greatest  extent  re- 
absorbed in  the  intestinal  canal. 

6.  The  iron  is  also,  to  some  extent,  reabsorbed;  part  of  it 
is  eliminated  with  the  fa?ces. 

7.  The  mucus  is  eliminated  with  the  faeces. 

In  my  last  lecture  I  stated  that  bile  is  secreted  contin- 
ually. The  flow  of  bile  in  the  channels  and  ducts  is  main- 
tained principally  by  the  following  factors  : 


154      LECTURES   ON    HUMAN    PHYSIOLOGY    AND    HISTOLOGY. 

1.  By  the  continual  activity  of  the  hepatic  cells. 

2.  By  the  mechanical  pressure  of  the  diaphragm  upon 
the  liver  during  the  respiratory  movements. 

3.  By  the  contraction  of  the  muscular  fibres  contained 
in  the  walls  of  the  larger  bile-ducts. 

A  resume  of  the  digestive  processes  which  take  place  in 
the  intestinal  canal  as  the  result  of  the  actions  of  the  three 
digestive  juices — viz.,  the  pancreatic  juice,  thesuccus  ente- 
ricus,  and  the  bile — upon  the  ingredients  of  the  chyme  may 
be  given  as  follows : 

1.  The  chyme,  which,  owing  to  the  presence  of  the  gas- 
tric juice,  is  acid,  is  rendered  alkaline  by  the  alkaline  salts 
of  the  pancreatic  juice. 

2.  The  pepsin  and  albuminates  are  precipitated  by  the 
biliary  acids. 

3.  Proteids  are  changed  into  peptones  by  the  proteolytic 
ferments  of  the  pancreatic  and  intestinal  juices. 

4.  Fats  are  separated  into  fatty  acids  and  glycerin  by 
the  action  of  steapsin. 

5.  Starches,  dextrin,  and  other  amylaceous  ingredients 
are  transformed  into  glucose  by  the  diastatic  ferments  of 
the  pancreatic  juice,  the  bile,  and  the  intestinal  juice. 

6.  Fats  are  emulsified  by  the  bile. 

7.  Cane-sugar,  lactose,  etc.,  are  converted  into  dextrose 
by  the  action  of  invertin. 

8.  The  intestinal  contents  are  diluted  by  the  water  of 
the  bile,  succus  entericus,  and  pancreatic  juice. 

From  the  foregoing  it  may  be  said  that  the  intestinal  di- 
gestion has  for  its  purpose  the  continuation  and  completion 
of  the  digestion  begun  in  the  stomach. 

Non-digested  or  indigestible  ingredients  of  the  food,  to- 
gether with  certain  excrementitious  matters,  are  conveyed 
onward  through  the  whole  intestinal  canal  by  the  peristal- 
tic contraction  of  its  muscular  fibres,  and  finally  these 
substances  are  eliminated  as  the  fceces  by  the  act  called 
defecation. 


THE   BILE.  155 

The  time  required  for  the  passage  of  the  intestinal  con- 
tents through  the  whole  intestinal  canal  is  from  12  to  24: 
hours;  during  this  period  the  folio vriug  processes  take  place: 

1.  The  digestion  of  unabsorhable  materials,  which  takes 
place  principally  in  the  small,  but  to  a  limited  extent  also 
in  the  large  intestines,  as  the  result  of  the  action  of  the 
secretions  of  the  foUicles  of  the  latter. 

2.  The  absorption  of  digested  materials;  this  also  takes 
place  principally  in  the  small  intestines.  The  raucous 
membrane  of  the  large  intestines  also  takes  up  rapidly 
easily  absorbable  materials,  such  as  water,  saline  solutions, 
etc. 

3.  Peristaltic  motions,  by  which  the  food  is  mixed  with 
the  digestive  juices,  and  b}^  which  the  contents  of  the 
small  intestines  are  conveyed  onward  in  the  intestinal 
canal. 

4.  Decomposition  and  putrefaction  of  ingredients  of  the 
intestinal  contents,  due  to  the  presence  of  micro-organisms 
which  are  introduced  into  the  alimentary  canal  with  the 
food  and  drink,  and  which,  by  their  growth  and  develop- 
ment, produce  fermentation  and  putrefaction  of  the  intes- 
tinal contents  with  the  production  of  fetid  gases  and  odors. 

The  micro-organisms   existing  in    the  intestinal   canal 
may  be  divided  as  follows : 
(a)  According  to  their  form  : 

Micrococci — round . 

Vihrions — spiral. 

Bacteria — rod-like,  short. 

Bacilli — rod-hke,  long. 
{h)  According  to  the  changes  they  produce,  into 

1.  Those  causing  fermentation: 

Bacterium  lactis. 
Bacterium  aceti. 
Bacterium  hutyricus. 

2.  Those  causing  the  division  of  albuminous  substances : 

Schizomycetes. 


156       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

3.  Those  causing  disease: 

Pathogenetic  bacteria. 

4.  Those  produciDg  poisons  in  the  intestinal  canal: 

Toxigenetic  bacteria. 

5.  Those  producing  coloring  matters: 

Chromogenetic  bacteria. 

6.  Those  producing  fetid  odors: 

Bromogenetic  bacteria. 

The  solid  products  of  the  decomposition  of  materials  of 
the  intestinal  contents  are  indol,  skatol,  and  phenol.  They 
are  organic  nitrogenized,  crystallizable  substances  formed 
during  the  decomposition  of  albuminous  and  albuminoid 
substances;  they  are  constant  ingredients  of  the  faeces  and 
give  to  them  the  characteristic  fecal  odor. 

The  gases  produced  as  the  result  of  the  decomposition  of 
ingredients  of  the  intestinal  contents  are:  carbon  dioxide 
(C0„),  sulphuretted  hydrogen  (H„S),  carburetted  hydrogen 
(CHJ,  and  hydrogen  (H). 

The  formation  of  the  faeces  takes  place  principally  in  the 
large  intestines.  The  intestinal  contents,  as  they  pass  on- 
ward toward  the  large  intestines,  assume  a  fetid  odor,  and 
often  an  acid  reaction  owing  to  the  formation  of  acids  as 
the  products  of  putrefaction  and  decomposition. 

In  the  beginning  the  fecal  matter  is  soft  and  semi-liquid, 
but  as  it  passes  on  and  reaches  the  lower  portion  of  the 
large  intestines  it  is  of  a  more  solid  consistence,  so  that  a 
mass  forms  which  assumes  the  shape  of  the  interior  of  the 
bowel.  The  firm  consistence  of  the  fecal  masses  in  the 
lower  part  of  the  large  intestines  is  due  to  the  fact  that 
during  their  passage  through  to  the  large  intestines  water 
and  soluble  ingredients  are  absorbed  from  them,  and  to  the 
fact  that  the  property  of  absorption  of  the  mucous  mem- 
brane of  the  large  intestines  is  greater  than  its  property  of 
secretion. 

The  digestive  juice  secreted  by  the  follicles  of  the  mucous 
membrane  of  the  large  intestines  is  scanty  and  very  tena- 
cious, owing  to  the  great  quantity  of  mucus  it  contains. 


DEFECATION.  157 

The  quantity  of  fecal  matter  formed  in  twenty-four 
hours  varies  with  the  quantity  and  quahty  of  food  taken. 
Ordinarily  it  is  from  150  to  250  grammes;  it  is  greater 
when  vegetable  foods  are  taken  than  it  is  when  meat  con- 
stitutes the  principal  ingredient  of  the  food.  The  composi- 
tion of  the  faeces  also  varies  with  the  character  of  the  food 
taken.  Normally  it  is  composed  of  water  70  to  80  per  cent, 
solids  20  to  30  per  cent. 

The  solids  are:  1.  Indigestible  ingredients  of  the  food, 
such  as  cellulose,  cartilage,  elastic  fibres,  fibres  from  vege- 
tables, etc. 

2.  Non -digested  ingredients  of  the  food  which,  owning  to 
their  preparation  or  insufficient  mastication,  were  incom- 
pletely digested  or  not  digested  at  all  during  their  passage 
through  the  alimentary  canal. 

3.  Salts  which  are  not  easily  absorbed,  or  which  with 
others  form  insoluble  compounds — phosphates  of  calcium 
and  magnesium,  small  portions  of  iron,  etc. 

4.  Decomposition  products  of  albuminous  or  albuminoid 
substances — indol,  skatol,  phenol. 

5.  Mucus. 

6.  Products  of  the  decomposition  of  the  specific  bile-ingre- 
dients in  the  intestinal  canal — stercobilin  and  hydrobiliru- 
bin,  formed  from  the  bile-pigments;  traces  of  biliary  acids. 

7.  Cholesterin  and  lecithin  from  the  bile. 

8.  Fat,  when  such  has  been  taken  in  excess  with  the 
food. 

9.  Acids  which  are  formed  during  decomposition  and 
fermentation  in  the  intestinal  canal,  such  as  lactic  acid, 
butyric  acid,  etc. 

10.  Gases— CO,,  NH„  H,S,  CH„  and  H. 

11.  Bacteria. 

7.  Defecation. 

Defecation  is  the  act  by  which  the  faeces  are  eliminated 
from  the  intestinal  canal.  The  contents  of  the  intestines 
pass  through  the  small  intestines  in   about  three  hours, 


158       LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

and  then  in  about  twelve  hours  through  the  large  intes- 
tines. The  intestinal  contents  are  moved  onward  by  the 
peristaltic  contractions  of  the  muscular  fibres. 

The  peristaltic  action  of  the  small  intestines  is  more 
active  than  that  of  the  large. 

The  lower  part  of  the  rectum  is  guarded  by  two  muscles, 
called  the  internal  and  the  external  sphincter  ani;  the  first 
is  an  involuntary,  and  the  second  a  voluntary  muscle. 

The  act  of  defecation  is  a  reflex,  but  also  a  voluntary 
nervous  act.  The  collection  of  fasces  in  the  lower  part  of 
the  rectum  produces,  by  its  irritating  effect  on  the  sensory 
nerve-fibres  of  the  mucous  membrane  of  the  rectum,  the 
desire  to  defecate;  the  stimulus  is  conveyed  to  the  brain 
and  to  the  centre  of  defecation,  which  is  located  in  the  spi- 
nal cord  in  the  lumbar  region.  The  response  to  the  stimu- 
lus is  a  relaxation  of  the  sphincter  ani  internus.  By  con- 
tracting the  external  sphincter  ani  the  escape  of  faeces  can 
be  prevented  for  a  time,  until  the  strain  to  which  that 
muscle  is  subjected  by  the  constant  pressure  of  the  faeces 
from  within  is  too  great  and  overcomes  the  voluntary  con- 
traction of  the  muscle,  and  an  involuntary  escape  of  the 
faeces  is  the  result.  Immediately  after  the  act  of  defeca- 
tion the  sphincters  contract  for  a  while.  As  long  as  there 
are  no  faeces  in  the  rectum  the  sphincters  are  not  con- 
tracted, but  the  elasticity  of  the  soft  parts  surrounding  the 
lower  portion  of  the  rectum  and  its  external  opening,  the 
anus,  is  sufficient  to  close  the  latter. 

The  centripetal  or  sensory  aerves  for  the  act  of  defeca- 
tion are  from  the  hemorrhoidal  and  from  the  inferior  me- 
senteric plexus. 

The  contrifugal  or  motor  nerves  are  from  the  pudic 
plexus  and  are  distributed  to  the  sphincters. 

When  the  act  of  defecation  is  performed  by  an  effort  of 
the  will  the  external  sphincter  is  relaxed,  and  the  muscles 
of  the  abdominal  walls  are  contracted  to  aid  by  their  pres- 
sure in  the  expulsion  of  the  faeces. 


QUESTIONS  AND   EXERCISES.  159 

QUESTIONS   AND   EXERCISES. 

Subject. — Digestion. 

Lectures  XIL-XVIII.  inclusive. 

252.  What  is  meant  by  digestion  ? 

253.  Name  the  organs  composing  the  digestive  apparatus. 

254.  Name  the  stages  of  digestion. 

255.  Name  the  mechanical  processes  of  digestion. 

256.  Name  the  chemical  processes  of  digestion. 

257.  Name  the  various  portions  of  the  aUmentary  canal. 

258.  Name  the  digestive  juices. 

259.  Describe  the  act  of  prehension. 

260.  Name  the  number  of  permanent  and  temporary 
teeth  in  the  human  being. 

261.  Give  the  periods  of  eruption  of  the  temporary  and 
the  permanent  teeth. 

262.  When  does  the  development  of  the  temporary  and 
when  does  that  of  the  permanent  teeth  begin  ? 

263.  Describe  the  process  of  the  development  of  the  tem- 
porary teeth. 

264.  Describe  the  process  of  the  development  of  the  per- 
manent teeth. 

265.  What  causes  the  shedding  of  the  temporary  teeth  ? 

266.  What  is  the  difference  in  the  form  of  the  human 
teeth  and  those  of  the  carnivora  and  those  of  the  herbi- 
vora  ? 

267.  Why  is  the  alveolar  process  of  the  jaws  not  repaired, 
like  all  other  bony  tissues,  after  fracture,  etc.  ? 

268.  AVhat  is  the  percentage  of  animal  and  of  earthy  mat- 
ter in  enamel,  dentin,  cementum  ? 

269.  What  is  pericementum? 

270.  Name  and  describe  the  motions  by  which  mastica- 
tion is  effected. 

271.  Name  the  muscles  which  produce  the  motions  re- 
quired for  mastication,  and  describe  their  action. 

272.  Describe  the  nervous  mechanism  of  the  act  of  mas- 
tication. 


160      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

273.  What  is  the  function  of  the  dental  periosteum  ? 

274.  Describe  the  formation  of  dentin  and  enamel. 

275.  Draw  a  vertical  section  of  a  tooth,  indicating  by 
name  the  various  parts.     Describe  each  part. 

276.  At  what  period  of  life  is  the  development  of  teeth 
first  indicated  ? 

277.  Define  calcification. 

278.  Give  the  process  of  replacement  of  temporary  by 
permanent  teeth. 

279.  Name  the  glands  of  the  mouth.  How  are  they  clas- 
sified ? 

280.  Name  the  salivary  glands.  To  what  class  of  glands 
do  they  belong,  according  to  their  structure  ? 

281.  Describe  the  anatomy  and  structure  of  the  parotid 
glands,  their  blood  and  nerve  supply,  their  minute  struc- 
ture, and  the  quality  of  their  secretion. 

282.  Give  the  anatomy  and  minute  structure  of  the  sub- 
maxillary glands,  and  describe  the  quality  of  their  secre- 
tion. 

283.  Give  the  anatomy  and  minute  structure  of  the  sub- 
lingual glands,  and  describe  the  quality  of  their  secretion. 

284.  Name  and  describe  the  ducts  of  the  salivary  glands. 

285.  Give  the  composition  of  human  saliva, 

286.  Describe  the  mode  of  secretion  of  saliva. 

287.  What  are  the  properties  of  saliva  ? 

288.  What  is  the  effect  of  saliva  on  starch  ? 

289.  What  are  the  reaction  and  specific  gravity  of  saliva  ? 
How  is  this  reaction  tested  ? 

290.  What  would  be  the  effect  on  the  saliva  and  on  di- 
gestion if  8tenson's  duct  were  divided  ? 

291.  Describe  the  nervous  mechanism  of  the  secretion  of 
saliva. 

292.  What  is  the  average  quantity  of  saliva  secreted  in 
twenty-four  hours  by  the  healthy  human  adult  ? 

293.  What  drugs  increase  and  what  drugs  decrease  the 
flow  of  saliva  ? 


QUESTIONS   AND   EXERCISES.  161 

294.  Name  the  ferment  of  the  sahva.    Describe  its  action. 

295.  Name  the  organs  concerned  in  the  act  of  deglu- 
tition. 

296.  Name  the  muscles  which  form  the  tongue. 

297.  Name  the  muscles  of  the  soft  palate. 

298.  Describe  the  pharynx. 

299.  With  what  cavities  does  the  pharynx  communicate? 

300.  Describe  the  oesophagus. 

301.  Through  what  opening  in  the  diaphragm  does  the 
oesophagus  pass  ? 

302.  Describe  the  epithelial  covering  of  the  mucous  mem- 
brane lining  the  buccal,  pharyngeal,  and  oesophageal  cavi- 
ties. 

303.  Describe  the  stages  of  deglutition. 

304.  How  is  the  food  prevented  from  entering  the  laryn- 
geal cavity  and  the  upper  respiratory  passages  during  the 
act  of  deglutition  ? 

305.  Describe  the  nervous  mechanism  of  the  act  of  deg- 
lutition. 

306.  What  is  the  stomach,  and  where  is  it  located  ? 

307.  Give  the  relations  of  the  stomach  to  the  viscera  sur- 
rounding it. 

308.  Describe  the  measurements,  shape,  opening,  and  the 
various  anatomical  points  of  the  stomach. 

30'J.  Name  the  nerves  and  blood-vessels  supplying  the 
stomach. 

310.  Name  the  coats  composing  the  walls  of  the  stomach. 

311.  Describe  the  arrangement  of  the  muscular  fibres  of 
the  stomach. 

312.  Describe  the  structure  of  the  mucous  coat  of  the 
stomach. 

313.  Describe  the  glands  of  the  stomach. 

314.  Describe  the  motions  of  the  stomach. 

315.  Give  the  reaction,  specific  gravity,  and  composition 
of  the  gastric  juice. 

316.  Name  the  specific  ingredients  of  the  gastric  juice. 

11 


163     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY- 

317.  What  is  pepsin,  and  how  can  it  be  obtained  from 
gastric  juice  ? 

318.  Where  and  how  is  pepsin  found  ? 

319.  In  what  does  pepsin  differ  from  the  proteolytic  fer- 
ments ? 

320.  Where  and  how  is  HCl  of  the  gastric  juice  formed  ? 

321.  What  is  the  quantity  of  free  HCl  in  the  gastric 
juice  ? 

322.  What  are  the  properties  and  functions  of  the  gas- 
tric juice  { 

323.  Describe  the  mode  of  secretion  of  gastric  juice,  and 
the  approximate  quantity  ordinarily  secreted  by  a  healthy 
human  adult  in  twenty-four  hours. 

324.  What  is  the  effect  of  alcohol  on  the  gastric  diges- 
tion (    What  is  the  average  duration  of  gastric  digestion  ? 

325.  What  is  the  chyme  ?    Describe  its  composition. 

326.  What  is  the  effect  of  gastric  juice  upon  cooked 
meats,  fried  or  broiled  meats,  raw,  soft,  and  hard-boiled 
eggs,  bread,  adipose  tissue,  bone,  cartilage,  elastic  tissue, 
fat,  sugar,  starches,  and  vegetables  ? 

327.  Describe  the  physiology  of  vomiting. 

328.  Name  the  digestive  juices  which  are  poured  into  the 
small  intestines. 

329.  Give  the  names  of  the  various  portions  of  the  small 
and  the  large  intestines. 

330.  Give  the  coats  which  form  the  walls  of  the  intesti- 
nal canal. 

331.  Describe  the  arrangement  of  the  muscular  fibres  in 
the  walls  of  the  small  and  the  large  intestines. 

332.  Describe  the  mucous  membrane  of  the  small  intes- 
tines. 

333.  What  are  the  villi  ?    Where  are  they  found  ? 

334.  What  are  solitary  glands,  and  agminate  glands  or 
Peyer's  patches,  and  where  are  they  found  ? 

335.  Name  and  describe  the  secreting  glands  of  the  in- 
testinal canal. 


QUESTIONS   AND   EXERCISES.  163 

336.  Give  the  nerve  and  blood  supply  to  the  intestines. 

337.  Give  the  reaction,  specific  gravity,  and  composition 
of  the  succus  entericus. 

338.  Name  the  digestive  properties  of  the  succus  enteri- 
cus. 

339.  Describe  the  pancreas. 

340.  Give  the  specific  gravity  and  reaction  of  pancreatic 
juice. 

341.  Give  the  composition  of  pancreatic  juice. 

342.  Name  the  ferments  of  the  pancreatic  juice  and  their 
actions. 

343.  Describe  the  mode  of  secretion  of  pancreatic  juice. 

344.  Give  a  resume  of  pancreatic  digestion. 

345.  ^t  what  point  does  the  duct  of  the  pancreas  open 
into  the  intestinal  canal  ? 

346.  Where  is  the  bile  secreted  ? 

347.  Name  the  fissures,  lobes,  ligaments,  and  coverings 
of  the  liver,  and  give  the  average  weight  and  measure- 
ments of  that  organ. 

348.  What  is  Glisson's  capsule  ? 

349.  Describe  the  fiver  lobule  and  the  structural  elements 
composing  it. 

350.  Describe  the  portal  circulation. 

351.  Describe  the  course  of  the  hepatic  artery  and  that 
of  the  hepatic  veins. 

352.  Describe  a  hepatic  cell  and  give  its  composition. 
358.  Describe  the  course  of  the  bile-ducts. 

354.  Name  the  structures  contained  in  a  portal  canal. 

355.  Give  the  specific  gravity,  reaction,  and  color  of 
human  bile. 

356.  What  is  the  average  quantity  of  bile  secreted  by 
man  in  twenty-four  hours  ? 

357.  Give  the  composition  of  the  bile. 

358.  Name  and  describe  the  specific  ingredients  of  the 
bfie. 

359.  Give  Pettenkofer's  test  for  bile-salts. 


X64      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

360.  Give  Gmelin's  test  for  bile-pigments. 

361.  How  are  the  ingredients  of  the  bile  formed  in  tho 
liver  ?  Explain.  Give  reasons  to  substantiate  your  state- 
ment. 

362.  Name  conditions  which  influence  the  secretion  of 
the  bile. 

363.  Describe  the  mode  of  the  secretion  of  the  bile,  and 
state  its  course  to  the  intestinal  canal. 

364.  Name  conditions  influencing  the  flow  of  bile. 

365.  What  are  the  uses  of  bile  ?    Describe  in  detail. 

366.  What  is  the  final  destination  of  bile  in  the  intestinal 
canal  ? 

367.  What  is  icterus  ? 

368.  What  is  hsemogenetic  and  what  is  hepatogenetic 
icterus  ? 

369.  Name  some  conditions  resulting  from  obstruction 
of  the  bile-ducts. 

370.  Give  a  resume  of  the  digestive  processes  in  the  intes- 
tinal canal. 

371.  Discuss  bacteria  in  the  intestines. 

372.  Describe  the  peristaltic  movements  of  the  intestines. 

373.  Describe  the  digestive  changes  in  the  large  intestines. 

374.  What  would  be  the  efl'ect  on  the  intestinal  digestion 
if  the  pancreatic  duct  were  obstructed  ? 

375.  What- conditions  favor  gastric  digestion  ? 

376.  Describe  the  digestion  in  the  stomach  of  a  meal  of 
bread  and  milk. 

377.  Name  the  ferments  that  are  essential  constituents 
of  each  digestive  fluid. 

378.  Describe  the  digestion  of  a  meal  of  eggs  and  beef. 

379.  Give  the  composition  of  normal  faeces. 

380.  State  the  average  weight  of  the  faeces  in  twenty- 
four  hours  in  a  normal  condition  of  health.  What  pro- 
portion is  made  up  of  liquid  and  what  of  solid  ingredients  ? 

381.  How  do  bacteria  get  into  the  intestinal  canal,  and 
what  is  the  result  of  their  presence  there  ? 


QUESTIONS   AND   EXERCISES.  165 

382.  Name  the  gases  developed  in  the  intestinal  canal. 

383.  What  are  indol,  skatol,  phenol,  stercobihn,  hydro- 
bilirubin  ?  How  and  from  what  are  they  formed  in  the 
intestinal  canal  ? 

384.  What  is  the  time  required  for  the  passage  of  the  in- 
testinal contents  through  (a)  the  small  intestines,  (h)  the 
large  intestines  ? 

385.  Describe  the  nervous  mechanism  of  the  act  of  defe- 
cation. 


LECTUEE   XIX. 

ABSORPTION. 

By  the  term  absorption  is  meant  the  introduction  of  ma- 
terials into  the  circulation.  Absorption  takes  place  to  a 
greater  or  less  extent  from  all  parts  of  the  body,  from  the 
free  surfaces — viz.,  the  mucous,  serous,  and  synovial  mem- 
branes, and  the  skin— and  from  the  interstices  of  the  tissues. 

Absorption  from  the  surfaces  has  for  its  main  object  the 
taking  into  the  circulation  of  the  materials  intended  for 
the  nutrition  of  the  tissues;  it  takes  place  principally  from 
the  mucous  membrane  of  the  alimentary  canal.  Absorp- 
tion from  the  surfaces  often  plays  an  important  role  in  the 
repair  of  pathological  conditions;  in  acute  inflammatory 
diseases — for  instance,  in  acute  articular  rheumatism,  pleu- 
risy, peritonitis,  meningitis,  pericarditis,  etc. — there  is  often 
an  effusion  of  fluid  into  the  affected  serous  or  synovial 
cavities.  This  fluid  is  at  times  completely  resorbed  by 
the  membrane  forming  the  walls  of  the  cavity. 

Absorption  from  the  interstices  of  the  organs  and  tissues 
has  for  its  object  the  draining  of  the  superfluous  parenchy- 
matous fluid.  The  tissue  elements  receive  their  nutritive 
materials  through  the  blood;  its  plasma,  holding  in  solution 
the  required  nutritive  materials,  exudes  through  the  walls 
of  the  capillaries  into  the  interstices  of  the  tissues  and 
constitutes  the  parenchymatous  jluid:  the  tissue  elements 
take  from  it  the  materials  they  require  and  give  into  it 
their  waste  materials;  the  parenchymatous  fluid  is  then 
absorbed  and  returned  into  the  blood  circulation.  Absorp- 
tion from  the  interstices  is  very  active,  and  this  fact  is  used 
extensively  in  the  administration  of  medicines.     I  refer 


ABSORPTION.  167 

here  to  the  hypodermic  and  parenchymatous  injections 
when  a  rapid  effect  of  the  drug  employed  is  desired.  Ab- 
sorption from  the  surfaces  is  most  active  from  the  mucous 
membrane.  The  skin,  owing  to  the  kind  and  arrangement 
of  its  many  layers  of  epithelial  cells,  possesses  a  very  lim- 
ited property  of  absorption. 

The  absorption  of  the  nutritive  materials  which  are  con 
tained  in  the  food  and  drink  takes  place  from  the  surface 
of  the  mucous  membrane  of  the  alimentary  canal. 

The  food  contains  absorbable  and  non-absorbable  nutri- 
tive materials;  the  latter  are  made  absorbable  in  the  ali- 
mentary canal  by  the  process  of  digestion.  The  absorption 
in  the  alimentary  canal  begins  in  the  mouth,  but  is  more 
active  in  those  portions  of  the  canal  below  the  diaphragm, 
viz.,  in  the  stomach  and  intestines;  it  is  most  active  in  the 
small  intestines. 

The  structure  of  the  mucous  membrane  of  the  small  in- 
testine renders  it  particularly  well  adapted  for  absorption. 
Let  me  refer  to  the  following  points:  1.  The  mucous 
membrane  of  the  small  intestines  is  arranged  in  transverse 
folds,  the  valvular  conniventes;  these  form  incomplete  circu- 
lar projections  into  the  lumen  of  the  intestinal  canal;  by  this 
arrangement  the  mucous  membrane  presents  a  larger  sur- 
face for  absorption,  and  a  too  rapid  passage  of  the  contents 
through  the  intestines  is  prevented.  2.  The  mucous  mem- 
brane of  the  small  intestines,  like  that  of  the  whole  ali- 
mentary canal  below  the  cardiac  opening  of  the  stomach, 
is  covered  with  a  single  layer  of  cylindrical  epithelium,  be- 
neath which  the  capillaries  ramify.  3.  The  mucous  mem- 
brane of  the  small  intestines  presents  numerous  minute, 
cone-like  elevations  called  villi;  they  give  to  the  mucous 
membrane  of  the  small  intestines  a  velvety  appearance. 
The  structure  of  the  villi  makes  them  special  organs  of 
absorption. 

A  villus  is  conical  in  shape,  from  3  to  5  millimetres  long, 
and  has  the  following  structure:    In  the  centre  there  is  a 


168     LECTURES   OX   HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

longitudinal,  delicate  vessel,  beginning  in  a  pouch  like  ex- 
pansion near  the  apex  of  the  villus,  and  communicating 
at  the  base  with  the  delicate  lymph-channels  beneath  the 
epithelial  layer;  this  delicate  vessel  is  called  the  lacteal. 
The  lacteals  are  the  beginnings  of  the  lymphatics  of  the 
small  intestines.  The  lacteal  is  surrounded  by  a  layer  of 
non-striated  muscular  fibres;  outside  of  this  is  a  network 
of  areolar  and  adenoid  tissue  which  contains  numerous 
large  lymphoid  cells  in  its  meshes.  This  areolar  and  ade- 
noid network  forms  the  matrix  of  the  villus;  it  supports 
a  plexus  of  capillary  nerve-fibrilla^  and  the  lacteal.  The 
external  covering  of  the  villus  consists  of  delicate  basement 
membrane  covered  with  a  single  layer  of  cylindrical  epithe- 
lial cells;  the  free  border  of  these  cells  presents  a  striated 
appearance  and  is  called  the  striated  basilar  border.  The 
villus  receives  blood  by  a  delicate  arteriole  which  enters 
the  villus  at  one  side  of  its  base;  the  blood  is  carried  off  by 
a  veinule  which  leaves  the  villus  at  its  base  opposite  the 
point  where  the  arteriole  enters;  in  the  matrix  of  the  villus 
the  blood-vessels  form  a  capillary  plexus. 

The  absorption  of  mateiials  into  the  circulation  takes 
place  through  the  walls  of  the  blood-  and  lymph -capillaries. 
The  materials  absorbed  into  the  blood-capillaries  are  con- 
veyed by  the  blood-circulatory  system  to  their  point  of 
destination.  The  materials  absorbed  into  the  lymph-capil- 
laries are  carried  by  the  lymph-vessels  through  lymphatic 
glands,  and  are  finally  emptied  into  the  blood-circulatory 
system.  The  blood-circulatory  system  consists  of  the 
heart,  arteries,  capillaries,  and  veins. 

The  blood-capillaries  are  freely  distributed  through  the 
tissues  and  organs;  their  walls  consist  of  a  single  layer  of 
large,  nucleated,  polygonal  endothelial  cells  continuous 
with  the  endothelial  lining  of  the  arteries  and  veins. 

The  capillaries  anastomose  between  the  structural  ele- 
ments of  the  tissues.  The  blood-capillaries  of  the  stomach 
and  intestinal  canal  are  located  beneath  the  epithelial  layer. 


ABSORPTION.  1G9 

The  blood  of  the  stomach  and  intesdnal  canal,  which  con- 
tains the  materials  absorbed  into  the  capillaries  in  these 
locations,  is  conveyed  by  the  gastric,  splenic,  the  superior 
mesenteric,  and  the  inferior  mesenteric  veins  into  the  por- 
tal vein,  by  which  it  is  carried  into  the  liver. 

The  lymphatic  system  consists  of  lymph-capillaries, 
lymph-vessels,  and  lymphatic  glands.  The  lymph-capil- 
laries are  delicate  vessels,  the  walls  of  which  are  composed 
of  a  thin,  fibrous  membrane  lined  with  a  single  layer  of 
endothelial  cells.  The  lymph-capillaries  begin  in  various 
ways:  1.  From  lymph-spaces,  which  are  small  lacunar 
openings  or  cavities  contained  in  the  connective  tissues. 
2.  From  perivascular  spaces,  which  are  situated  betvv^een 
the  delicate  capillary  blood-vessels  in  the  nerve-centres, 
bone-tissue,  etc.  3.  From  stomata,  which  are  small,  angu- 
lar spaces  between  the  epithelial  cells  covering  the  walls 
of  the  serous  aud  synovial  cavities.  4.  From  the  lacteals, 
which  are  the  beginnings  of  the  lymph-capillaries  of  the 
small  intestines. 

The  lymphatic  vessels  convey  the  material  taken  by 
the  lymph-capillaries  through  the  lymphatic  glands  into 
the  blood  circulation.  The  lymph-vessels,  like  the  blood- 
vessels, have  a  varying  calibre.  Their  walls  are  composed 
of  three  coats — namely,  an  external  coat,  which  is  composed 
of  areolar  tissue  and  non-striated  muscular  fibres;  a  mid- 
dle coat,  composed  of  muscular  and  elastic  fibres;  and  an 
internal  coat,  composed  of  a  single  layer  of  polygonal 
endothelial  cells.  The  interior  of  many  lymph-vessels  is 
provided  with  valves,  which  are  reduplications  of  the  endo- 
thelial lining  and  are  intended  to  prevent  a  regurgitation 
of  the  lymph.     They  are  most  abundant  near  the  glands. 

The  lymp)hatic  glands  are  small,  oval  masses  of  adenoid 
tissue  interposed  in  the  course  of  the  lymph-vessels. 
Lymphatic  glands  are  found  in  the  vicinity  of  the  large 
abdominal  and  thoracic  vessels,  and  in  the  regions  of  the 
neck,  axilla,  elbow,  in  the  groin,  and  in  the  popliteal  space. 


170     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  solitary  or  Peyer's  glands  contained  in  the  submucosa 
of  the  intestinal  canal,  and  the  glands  of  the  mesenteric, 
are  also  lymphatic  glands.  A  lymphatic  gland  consists  of 
a  convex  and  a  concave  portion;  the  latter  is  termed  the 
hilus.  The  whole  gland  is  covered  with  a  capsule  composed 
of  fibrous  tissue  and  non-striated  muscular  fibres;  from 
this  capsule  prolongations  are  sent  into  the  substance  of 
the  gland,  dividing  it  into  compartments  or  alveoli;  these 
fibrous  structures  constitute  the  cortical  portion  of  the 
gland.  The  alveoli  are  filled  with  adenoid  tissue  contain- 
ing lymph-corpuscles ;  these  structures  constitute  the 
medullary  portion  of  the  gland.  The  lymphatic  vessels 
enter  at  the  cortical  portion;  their  contents  pass  through 
the  network  of  the  medullary  portion,  and  finally  leave 
the  gland  by  a  vessel  which  passes  out  at  the  hilus.  The 
contents  of  the  lymphatics,  called  the  lymph,  are  conveyed 
into  the  blood-circulatory  system.  The  lymph  from  the 
lower  part  of  the  body — namely,  from  the  lower  extremi- 
ties, the  pelvis  and  pelvic  viscera,  the  abdomen  and  abdo- 
minal viscera — also  the  lymph  from  the  small  intestines,  is 
collected  in  the  receptaculiim  chyli.  This  is  a  triangular 
pouch  situated  in  the  abdominal  cavity  in  front  of  the  sec- 
ond lumbar  vertebra;  its  coats  are  composed  of  fibrous 
tissue  containing  elastic  and  non-striated  muscular  fibres; 
from  this  the  lymph  is  conveyed  by  a  vessel,  the  thoracic 
duct,  into  the  blood  circulation. 

The  thoracic  duct  is  a  lymph- vessel,  about  18  inches 
long,  which  passes  through  the  aortic  opening  in  the  dia- 
phragm, ascends  into  the  posterior  mediastinum  of  the 
thoracic  cavity,  and  finally  opens  into  the  subclavian  vein 
at  its  junction  with  the  left  internal  jugular  vein.  The 
thoracic  duct  is  supplied  with  numerous  valves;  during  its 
course  through  the  thoracic  cavity  it  receives  the  lymph 
from  the  thoracic  viscera. 

The  lymph  of  the  right  upper  part  of  the  body  is  con- 
veyed by  a  short  duct,  the  right  lymphatic  duct,  into  the 


ABSORPTION.  171 

venous  circulation  ;  it  opens  into  the  right  subclavian  vein 
at  the  point  of  junction  of  that  vessel  with  the  right  in- 
ternal jugular  vein.  The  fluid  circulating  in  the  lymph- 
atic system  is  called  the  Iijinph. 

TJie  physical  properties  and  composition  of  lymph  are  as 
follows  :  Lymph  is  a  colorless  alkaline  fluid,  which  has  no 
odor,  a  saline  taste,  and  a  specific  gravity  of  1012  to  1020. 
Lymph  is  composed  of  lymph-plasma  and  lymph-corpuscles. 

Lymph-plasma  is  identical  with  blood-plasma;  it  is  com- 
posed of  water,  inorganic  salts,  serum-albumin,  and  alka- 
line-albumin ;  it  also  contains  fibrin-forming  substances 
which  cause  lymph  to  coagulate  slowly  into  a  jelly-like 
mass  when  exposed  to  air.  Lymph-plasma  is  the  fluid 
w^hich  exudes  through  the  walls  of  the  capillaries  into  the 
interstices  of  the  tissues. 

Lymph-corpuscles  are  large,  nucleated,  spherical  cells 
identical  with  leucocytes.  They  originate  in  the  lymph- 
atic glands  and  in  the  organs  which  in  this  structure  con- 
tain adenoid  tissue.  This  is  shown  by  the  fact  that  the 
lymph-capillaries  do  not  contain  lymph-corpuscles,  and 
that  the  lymph  in  a  vessel  leaving  a  lymphatic  gland  con- 
tains a  greater  number  of  lymph-corpuscles  than  the  lymph 
in  the  vessel  entering  the  gland. 

The  physiological  functions  of  the  lymiDh-corpuscles  were 
described  in  the  remarks  on  the  leucocytes. 

The  lymph  contained  in  the  lymphatics  of  the  small  in- 
testines is  called  the  chyle,  from  the  milky  appearance 
which  it  assumes  by  its  mixture  with  the  fat  which  is  ab- 
sorbed by  the  lacteals  in  the  small  intestines.  Chyle, 
therefore,  is  lymph  plus  fat. 

The  factors  which  maintain  the  circulation  of  the  lymph 
are  the  following : 

1.  The  force  exerted  from  behind  by  the  materials  which 
are  constantly  taken  up  by  the  lymph-capillaries. 

2.  The  contraction  of  the  muscular  fibres  of  the  walls  of 
the  lymphatic  vessels. 


173      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

3.  The  contraction  of  voluntary  muscles. 

4.  The  respiratory  movements. 

5.  Nerve  influence. 

6.  The  valves  in  the  interior  of  the  lymph-vessels  which 
prevent  a  regurgitation  of  the  lymph. 

The  amount  of  lymph  circulating  in  the  system,  and  the 
amount  of  lymph  which  is  poured  into  the  blood  circula- 
tion in  twenty-four  hours,  has  been  estimated  to  be  equal 
to  the  amount  of  blood  in  the  body.  The  rapidity  of  the 
circulation  is  very  much  slower  than  that  of  the  blood. 

The  lymphatic  glands  are,  as  I  have  stated  before,  the 
organs  in  which  lymph-corpuscles  originate ;  they  are 
formed  as  the  product  of  the  elaboration  of  materials  by 
the  glands.  The  lymphatic  glands  serve  another  very  im- 
portant purpose  :  through  them  the  lymph  is  filtered  in  its 
course  to  the  blood  circulation,  and  materials  are  often  re- 
tained the  introduction  of  which  into  the  blood  circulation 
would  be  the  cause  of  disease.  Poisons,  pathogenic  sub- 
stances, and  bacteria  are  often  absorbed  by  the  lymphatics 
and  retained  in  the  lymphatic  glands,  as  is  shown  by  their 
enlargement  in  many  infections — for  example,  in  syphilitic 
and  tubercular  infections. 


LEOTUEE   XX. 
ABSORPTION  {continued). 

The  absorption  of  nutritive  materials  takes  place  in  the 
alimentary  canal  through  the  walls  of  the  delicate  blood- 
and  lymph-vessels. 

As  the  factors  which  effect  the  absorption,  must  be  con- 
sidered, first,  the  special  physiological  function  of  the 
epithelial  lining  of  the  alimentary  canal,  and,  second,  phy- 
sical forces — viz.,  diffusion,  endosmosis,  and  filtration. 

The  diffusion  of  liquids  is  a  physical  process,  consisting 
in  the  tendency  of  two  or  more  liquids  contained  in  a  ves- 
sel to  mingle  until  an  equal  mixture  of  the  liquids  in  the 
vessel  has  taken  place.  The  diffusion  of  liquids  takes  place 
independent  of  their  specific  weights  and  pressure.  A  dif- 
fusion can  occur  only  between  liquids  which  are  capable 
of  forming  a  mixture;  it  is  for  this  reason  impossible  be- 
tween two  liquids  like  oil  and  water. 

Endosmosis  is  a  physical  process  which  consists  in  the 
tendency  of  the  particles  of  two  or  more  liquids  contained 
in  a  vessel  and  separated  by  a  porous  membrane  to  mix 
through  the  pores  of  the  animal  membrane  until  an  equal 
mixture  of  the  liquids  has  taken  place. 

Endosmosis  takes  place  only  between  liquids  which  are 
capable  of  a  mixture;  it  takes  place  independent  of  any 
pressure  and  independent  of  the  specific  gravity  of  the 
liquids.  During  the  endosmosis  of  liquids  an  exchange  of 
all  substances  occurs  which  are  dissolved  in  the  liquids 
and  which  readily  pass  through  animal  membrane;  such 
substances  are  termed  crystalloids,  in  contradistinction 
to  substances  which    do    not   readily  pass    through  the 


J 7-4     LECTURES   ON    HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

pores   of   animal   membi-anes   and   which  are  called   col- 
loids. 

The  endosmotic  current  is  not  always  the  same  between 
the  particles  of  different  liquids,  but  it  depends  upon  the 
nature  of  the  liquids  and  the  diffusibility  of  the  substances 
contained  in  them.  The  rule  is  that  the  current  always 
flows  from  that  side  of  the  animal  membrane  where  the 
liquid  is  more  easily  diffusible  to  that  side  of  the  membrane 
where  the  liquid  is  less  easily  diffusible.  By  diffusibility 
is  meant  the  power  of  a  liquid  to  pass  through  the  pores  of 
an  animal  membrane. 

The  diffusibility  of  a  liquid  depends  largely  upon  the 
character  of  the  substances  contained  in  it.  It  may  be 
said  that  the  absorption  of  the  nutritive  materials  in  the 
alimentary  canal  is  due  to  a  great  extent  to  an  endosmosis 
between  the  liquid  contained  in  the  intestinal  tract  and 
that  contained  in  the  lymph-  and  blood-vessels,  the  walls 
of  which  form  the  animal  membrane  through  which  the 
endosmosis  takes  place. 

The  direction  of  the  current  is  from  the  intestinal  canal 
into  the  lymph-  and  blood-vessels,  because  ordinarily  the 
liquid  in  the  alimentary  canal  passes  through  the  animal 
membrane  more  readily  than  the  liquid  contained  within 
these  vessels.  The  most  important  factor  of  this  direction 
of  the  current  must  be  considered  the  special  physiological 
property  of  the  epithelial  cells  covering  the  mucous  mem- 
brane of  the  alimentary  canal. 

Another  important  point  in  the  absorption  of  substances 
is  their  endosmotic  equivalent.  It  has  been  observed  that 
substances  contained  in  the  liquids  separated  by  an  animal 
membrane  are  often  exchanged  during  the  endosmotic 
current  for  a  certain  quantity  of  water  from  the  side 
toward  which  they  diffuse. 

The  quantity  or  weight  of  water  which,  during  the  en- 
dosmotic process,  is  exchanged  from  the  liquid  on  the  one 
side  of  the  animal  membrane  for  one  gramme  of  a  sub- 


ABSORPTION.  175 

stance  contained  in  the  liquid  on  the  other  side  of  the 
animal  membrane,  is  called  the  endosmotic  equivalent  of 
that  substance.  For  example,  the  endosmotic  equivalent 
of  sodium  chloride  is  4.  To  illustrate  this  we  will  take  a 
vessel  which  contains  two  hquids  separated  by  an  animal 
membrane,  one  of  which  is  distilled  water,  the  other  a  so- 
lution of  sodium  chloride.  During  the  endosmotic  process 
through  the  animal  membrane  4  cubic  centimetres  of  dis- 
tilled water  will  pass  toward  the  sodium  chloride  solution 
for  each  gramme  of  this  salt  which  passes  from  its  solution 
toward  the  distilled  water  on  the  other  side  of  the  animal 
membrane.  Ordinarily  the  substances  which  we  take  with 
the  food  and  drink  do  not  possess  a  higher  endosmotic 
equivalent  than  the  substances  contained  in  the  fluid  in  the 
lymph-  and  blood-vessels  into  which  they  are  absorbed, 
and  consequently  during  their  absorption  no  water  passes 
from  the  blood-  and  lymph-vessels  into  the  fluid  contents 
of  the  alimentary  canal. 

When  substances  are  introduced  into  the  alimentary 
canal  which  have  a  high  endosmotic  equivalent  their  ab- 
sorption then  causes  a  watery  effusion  into  the  ahmentary 
canal,  and  watery  diarrhoea  is  the  result.  Substances 
given  for  this  purpose  are:  sulphate  of  magnesium,  which 
has  an  endosmotic  equivalent  of  12;  sulphate  of  sodium 
and  potassium,  having  an  endosmotic  equivalent  of  from 
11  to  12.  Sugar,  which  has  an  endosmotic  equivalent  of  7, 
also  causes  watery  diarrhoea  when  taken  in  large  quanti- 
ties. 

The  endosmotic  equivalent  of  substances  is  not  always 
the  same;  it  is,  for  instance,  increased  when  the  substance 
is  well  diluted,  and  decreased  when  the  substance  is  in  a 
concentrated  solution;  it  increases  as  the  temperature  of 
the  solution  is  increased.  The  character  of  the  animal 
membrane  through  which  the  endosmosis  takes  place  also 
influences  the  endosmotic  equivalent  of  the  substances  con- 
tained in  solution. 


176    LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  filtration  of  liquids  is  a  physical  process  which  con- 
sists in  the  passing  of  the  liquids  through  the  pores  of  an 
animal  membrane  when  subjected  to  pressure. 

Filtration  depends  upon  the  amount  of  pressure  upon  the 
liquid;  upon  the  character  of  the  liquid  and  the  substances 
contained  in  it;  upon  the  degree  of  concentration  of  the 
solution;  and,  lastly,  upon  the  character  of  the  membrane 
through  which  the  fluid  is  filtered,  and  upon  the  tempera- 
ture of  the  liquid  to  be  filtered. 

The  filtration  of  liquids  is  more  active  when  the  animal 
membrane  is  porous,  when  the  liquid  has  a  good  affinity 
for  the  membrane,  when  the  substances  contained  in  the 
liquid  pass  readily  through  the  pores  of  the  animal  mem- 
brane, when  the  solution  of  the  substances  is  diluted,  and 
when  the  temperature  of  the  liquid  is  raised.  Colloids  con- 
tained in  liquids  to  be  filtered  do  not  pass  through  the 
pores  of  animal  membranes;  filtration  is  for  this  reason 
employed  to  separate  the  colloids  from  the  crystalloids 
contained  in  a  solution. 

The  introduction  of  substances  into  the  circulation  by 
the  process  of  filtration  takes  place  in  the  alimentary  canal 
when  its  muscular  walls  contract  and  thus  exert  a  pres- 
sure upon  the  intestinal  contents. 

From  the  foregoing  description  of  the  processes  which 
effect  absorption  it  can  be  clearly  understood  that  the  ab- 
sorption of  substances  depends  upon  various  conditions, 
which  may  be  enumerated  as  follows: 

1.  Upon  the  diffusibility  of  the  substances.  The  more 
readily  substances  pass  through  an  animal  membrane,  the 
quicker  they  are  absorbed;  colloid  substances  are  not  ab- 
sorbed . 

2.  Upon  the  density  of  the  liquid  and  the  grade  of  con- 
centration of  the  solution.  The  less  concentrated  a  solu- 
tion is,  the  quicker  it  is  absorbed. 

3.  Upon  the  condition  of  the  animal  membrane  through 
which  the  substances  are  absorbed. 


ABSORPTION.  177 

4.  Upon  the  tensiou  of  the  vessels  into  which  the  sub- 
stances are  absorbed.  By  the  tension  of  the  vessels  is 
meant  the  pressure  which  the  fluid  contained  in  them 
exerts  against  the  walls.  The  greater  the  tension  the  less 
rapidly  substances  are  absorbed. 

5.  Upon  the  rapidity  of  the  circulation  of  the  fluids  con- 
tained in  the  vessels  into  which  substances  are  absorbed. 
The  circulation  carries  away  the  fluid  and  the  absorbed 
materials  contained  in  it,  and  consequently  the  fluid  is 
constantly  renewed  for  the  reception  of  materials;  there- 
fore the  more  rapid  the  circulation  the  quicker  the  ab- 
sorption. 

6.  Upon  the  temperature  of  the  Hquids  to  be  absorbed, 
and  upon  the  endosmotic  equivalents  of  the  substances. 
The  absorbability  of  liquids  increases  with  an  increase  in 
their  temperature. 

Substances  having  a  high  endosmotic  equivalent  are 
best  absorbed  from  well-diluted  solutions. 

The  absorption  of  the  nutritive  materials  which  are 
taken  with  the  food  and  drink  takes  place,  as  I  have  stated, 
from  the  mucous  surface  in  all  parts  of  the  alimentary 
canal.  It  begins  in  the  mouth  to  a  very  limited  extent, 
owing  to  the  stratified  epithelial  covering  of  the  mucous 
membrane  of  the  buccal  cavity;  it  is  negative  in  the  pha- 
rynx and  oesophagus,  owing  to  the  rapidity  with  which  the 
food  passes  through  these  portions  of  the  alimentary  canal; 
it  is  more  active  in  the  stomach,  most  active  in  the  small 
intestines,  and  again  less  active  in  the  large  intestines. 

The  materials  in  the  alimentary  canal  are  absorbed  by 
the  blood-  and  lymph-vessels. 

Water  is  absorbed  principally  by  the  blood-vessels;  a 
small  amount  of  it  passes  into  the  lymphatics.  Water  is 
absorbed  quickly  and  completely. 

The  salts  are  also  absorbed  by  the  blood-vessels,  and,  to  a 
small  extent,  probably  by  the  lymphatics.  Salts  are  readily 
absorbed  only  when  in  a  weak  solution;  too  concentrated 

12 


178    LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

solutions  of  salts  cause  an  effusion  of  water  from  the  ves- 
sels into  the  intestinal  canal.  Sodium  chloride,  the  salt 
which  we  take  most  frequently,  is  readily  absorbed  as  long 
as  it  is  in  a  solution  not  exceeding  2  per  cent. 

The  carbohydrates  are  transformed,  by  the  process  of  di- 
gestion, into  sugars  which  readily  pass  through  animal 
membranes.  Sugars  are  absorbed  into  the  blood-vessels, 
very  little  by  the  lymphatics.  Sugars  having  high  endos- 
motic  equivalents  are  therefore  readily  absorbed  only  when 
in  a  weak  solution. 

The  albimiinous  substances  are  transformed  into  peptones; 
these,  in  the  slightly  acid  or  alkaline  liquid  of  the  stomach 
and  intestinal  contents,  are  readily  absorbed.  Peptones 
have  a  high  endosmotic  equivalent,  and  are  therefore  only 
absorbed  from  a  dilute  solution,  to  obtain  which  a  certain 
quantity  of  fluid  must  be  taken  with  the  food.  The  pep- 
tones are  absorbed  by  the  blood-vessels.  Proteids  are  col- 
loids and  are  therefore  not  absorbed. 

The  fats  which  are  taken  with  the  food  are  prepared  for 
absorption  in  the  small  intestines.  The  liberated  fat-  or 
oil-globules  are  here  split  up  by  the  steapsin  of  the  pan- 
creatic juice  into  fatty  acids  and  glycerin;  these  mix  with 
water  and  alkaline  salts  from  the  intestinal  juices,  and 
soap  is  thus  formed;  this,  with  the  bile,  forms  an  emulsion, 
in  which  are  contained  the  exceedingly  finely  divided  fat- 
and  oil-globules,  which  now  pass  into  the  lacteals  and  are 
thus  taken  up  into  the  lymph  circulation. 

The  method  by  which  the  fats  pass  into  the  lacteals  is 
not  fully  understood.  It  has  been  observed  that  during 
the  process  of  absorption  minute  fat-globules  are  contained 
in  the  epithelial  cells  covering  the  villi,  and  it  is  believed 
that  the  striae  of  the  basilar  border  of  the  epithelial  cells 
grasp  the  fat-globules,  and  that  these  are  passed  through 
these  cells  by  a  protoplasmic  movement.  It  has  further- 
more been  observed  that  the  large  lymphoid  corpuscles 
which  are  contained  in  the  adenoid  tissue  of  the  matrix  of 


QUESTIONS   AND   EXERCISES.  179 

the  villi  send  out  prolongations  from  their  bodies,  which 
pass  between  the  epithelial  cells  covering  the  villi  and  grasp 
the  fat-globules  and  convey  them  into  the  lacteals;  from 
these  they  are  forced,  by  the  contraction  of  the  muscular 
fibres  surrounding  each  lacteal,  into  the  lymph-channels 
in  the  walls  of  the  small  intestines,  where  they,  together 
with  the  lymph,  constitute  a  milky  fluid — the  chyle.  The 
fats  are  absorbed  only  by  the  lacteals  of  the  small  intes- 
tines. 

Absorption  from  the  large  intestines  is  less  effective;  the 
most  nutritive  materials  are  already  absorbed  in  the  small 
intestines.  Water,  and  easily  absorbable  substances  dis- 
solved in  water,  are  readily  absorbed  in  the  large  intestines. 
The  contents  of  the  small  intestine,  as  they  pass  into  the 
large  intestine,  are  quite  liquid,  but  become  more  and 
more  solid  as  they  descend  in  the  large  intestine,  owing  to 
the  absorption  of  the  water  in  this  part  of  the  alimentary 
canal.  In  pathological  conditions  where  feeding  by  the 
mouth  is  impossible,  easily  absorbable  nutritive  materials 
are  brought  by  means  of  rectal  injections  into  the  large 
intestines,  where  they  are  subjected  to  the  action  of  the 
digestive  juice  secreted  by  the  follicles  of  the  mucous  mem- 
brane of  the  large  intestines,  and  where  they  are  readily 
absorbed.  Rectal  medication  is  also  based  upon  the  com- 
paratively great  absorbing  power  of  the  mucous  membrane 
of  the  large  intestines. 


QUESTIONS   AND   EXERCISES. 

Subject. — Absorption. 
Lectures  XIX.  and  XX. 

386.  What  is  meant  by  the  term  absorption  ? 
38Y.  What  structures  make  up  the  blood-circulatory  sys- 
tem? 


180     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

388.  Describe  the  structure  of  a  blood-capillary. 

389.  What  structures  make  up  the  lymphatic  system  ? 

390.  Describe  a  lymph-capillary. 

391.  Name  the  various  ways  in  which  lymph-capillaries 
begin. 

392.  Describe  the  structure  of  a  lymphatic  vessel. 

393.  Describe  the  structure  of  a  lymphatic  gland. 

394.  What  is  adenoid  tissue  ? 

395.  Give  the  direction  of  the  current  in  the  lymph-cir- 
culatory system. 

396.  Trace  the  course  of  the  lymph  from  the  various 
parts  of  the  body  into  the  blood  circulation. 

397.  Name  the  factors  which  maintain  the  circulation  of 
the  lymph. 

398.  Give  the  properties  and  composition  of  the  human 
lymph. 

399.  Describe  a  lymph-corpuscle. 

400.  Where  do  the  lymph-corpuscles  originate  ?  Give 
reasons  to  substantiate  your  statement. 

401.  Where  are  the  constituents  of  the  lymph  derived 
from? 

402.  How  do  the  tissue  elements  receiv^e  their  nutrition 
from  the  blood  ? 

403.  What  is  the  parenchymatous  fluid  of  the  tissues 
and  organs  ? 

404.  What  is  chyle,  and  where  is  it  found  ? 

405.  Trace  the  course  of  the  chyle  into  the  blood. 

406.  Why  does  the  skin  possess  but  little  absorbing 
power  ? 

407.  Describe  the  structure  and  distribution  of  the  mu- 
cous, serous,  and  synovial  membranes. 

408.  Why  is  absorption  more  active  in  the  parts  of  the 
alimentary  canal  below  the  diaphragm  than  in  those 
above? 

409.  Why  is  absorption  from  the  small  intestines  more 
active  than  from  the  stomach  ? 


QL'ESTIONS   AND    EXERCISES.  181 

410.  Describe  the  structure  of  the  mucous  membrane  of 
the  small  intestines. 

411.  Describe  the  structure  of  a  villus. 

412.  What  is  a  lacteal  ? 

413.  Describe  where  and  by  what  the  water,  the  inor- 
ganic salts,  the  carbohydrates,  and  the  peptones  are  ab- 
sorbed. 

414.  Describe  how  the  fats  are  absorbed  by  the  lacteals. 

415.  What  do  you  understand  by  hypodermic  injections, 
parenchymatous  injections,  rectal  medication,  rectal  feed- 
ing 1 

416.  Discuss  the  absorbing  power  of  the  large  intestines. 

417.  What  do  you  understand  by  the  diffusion  of  liquids? 

418.  What  is  endosmosis  ? 

419.  What  is  filtration  ? 

420.  In  what  direction  is  the  endosraotic  current  between 
two  liquids  separated  by  an  animal  membrane  ? 

421.  Why  is  the  endosmotic  current  from  the  intestinal 
canal  into  the  lymph-  and  blood-vessels  ? 

422.  What  do  you  understand  by  the  endosmotic  equiva- 
lent of  a  substance  ? 

423.  How  does  the  degree  of  concentration  and  the  tem- 
perature affect  the  absorbability  of  substances  ? 

424.  What  are  colloid  and  what  are  crystalloid  sub- 
stances ? 

425.  Enumerate  and  describe  the  conditions  which  influ- 
ence and  regulate  absorption. 

426.  What  are  the  channels  of  absorption  ? 

427.  Discuss  the  physiology  of  rectal  feeding. 

428.  State  the  difference  between  lymph  and  chyle. 

429.  What  are  the  functions  of  the  lymphatic  glands  ? 

430.  How  do  the  products  of  digestion  enter  the  circula- 
tion \ 

431.  Describe  the  physiologic  process  by  which  the  bite 
of  a  venomous  snake,  or  a  hypodermic  injection  of  the 
virus,  causes  death. 


183     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

432.  Describe  the  process  of  absorption  of  a  meal  con- 
sisting of  bread  and  butter  and  ham,  and  mention  the 
digestive  changes  which  these  articles  of  food  must  first 
undergo. 

433.  How  does  the  circulation  of  the  lymph  and  blood 
influence  absorption  ?    Explain. 


LECTURE  XXI. 

BLOOD  CIRCULATION. 

The  blood  circulation  has  for  its  object  the  conveying  of 
nutritive  material  to  the  tissues,  the  carrying  of  the  waste 
materials  from  the  tissues,  and  the  distributing  of  warmth 
to  the  different  parts  of  the  body.  The  blood  circulates 
in  the  blood-circulatory  system,  which  consists  of  the 
heart,  the  arteries,  the  capillaries,  and  the  veins. 

To  understand  the  circulation  of  the  blood  it  is  essential 
to  be  thoroughly  familiar  with  the  structure  of  the  organs 
composing  the  blood-circulatory  system.  I  will  therefore 
describe  the  structure  of  these  organs. 

The  Heart. 

The  heart  is  a  hollow,  muscular  organ  situated  in  the 
thoracic  cavity  between  the  lungs  and  behind  the  lower 
portion  of  the  sternum.  It  is  conical  in  shape,  with  its 
base  directed  upward,  backward,  and  to  the  right.  The 
surface  of  the  heart  which  is  directed  toward  the  anterior 
chest  wall  is  convex,  and  formed  principally  by  the  walls  of 
the  right  ventricle,  also  by  a  small  portion  of  the  anterior 
wall  of  the  left  ventricle.  The  surface  directed  posteriorly 
is  flattened  and  rests  partly  on  the  diaphragm;  it  is  formed 
principally  by  the  walls  of  the  left  ventricle. 

The  base  of  the  heart  corresponds  to  the  space  between 
the  fifth  and  eighth  dorsal  vertebrae;  the  apex,  to  a  point 
in  the  fifth  intercostal  space  three-fourths  of  an  inch  to 
the  left  of  the  sternum  and  an  inch  below  the  left  nipple. 

The  heart  is  contained  in  a  closed  membranous  sac,  the 


184     LECTURES   ON    HUMAN  PHYSIOLOGY   AND   HISTOLOGY. 

pericardium,  which  consists  of  an  outer  fibrous  and  an  inner 
serous  layer ;  the  latter  covers  the  entire  surface  of  the 
heart,  and,  being  reflected,  forms  the  lining  of  the  whole 
pericardial  cavity. 

The  pericardium  is  attached  above  to  the  large  vessels; 
below,  to  the  central  tendon  of  the  diaphragm.  The  func- 
tion of  the  pericardium  is  the  prevention  of  friction  and 
the  facilitation  of  the  cardiac  movements. 

The  heart  is  hollow  in  all  mammalia,  and  in  man  its 
cavity  is  divided  by  a  longitudinal  muscular  septum  into 
two  lateral  halves  ;  and  each  lateral  half  is  again  divided 
by  a  transverse  septum  into  two  cavities,  one  of  which  is 
directed  toward  the  base,  the  other  toward  the  apex,  of 
the  heart. 

The  four  cavities  of  the  human  heart  are  called,  respec- 
tively, the  right  auricle  and  ventricle  and  the  left  auricle 
and  ventricle.  The  auricles  are  contained  in  the  basilar, 
the  ventricles  in  the  apical,  portions  of  the  heart. 

The  longitudinal  septum  separating  the  right  and  the 
left  cavities  is  complete ;  each  auricle,  however,  communi- 
cates with  the  ventricle  on  the  same  side  by  an  opening  in 
the  auric ulo- ventricular  septum. 

The  location  of  these  transverse  and  longitudinal  septa 
is  indicated  by  furrows  on  the  surface  of  the  heart;  these 
are  called  the  auriculo-ventricular  and  the  interventricular 
furrows. 

The  interior  of  the  heart  is  lined  by  a  membrane  which 
is  called  the  endothelium;  it  consists  of  a  layer  of  fibrous 
tissue,  a  layer  of  elastic  and  muscular  fibres,  and  a  single 
layer  of  flat,  elongated  cells  supported  by  a  delicate  base- 
ment membrane. 

The  blood  enters  and  leaves  the  heart  by  vessels  which 
open  into  its  various  cavities;  several  of  these  openings  are 
supplied  with  valves,  which  are  merely  reduplications  of 
endothelium;  they  serve  to  prevent  the  blood  from  flowing 
in  the  wrong  direction. 


THE   HEART.  185 

The  cavities  of  the  heart  differ  in  their  size,  form,  and 
structure. 

The  right  auricle  has  a  capacity  of  about  2  ounces;  it  is 
a  little  larger  than  the  left  auricle  and  its  walls  are  thin- 
ner. It  consists  of  a  main  cavity,  called  the  sinus  venosus, 
and  a  smaller  cavity,  the  triangular  accessory  portion, 
called  the  appendix  auriculce.  The  right  auricle  has  the 
following  openings: 

1.  The  opening  of  the  superior  vena  cava.  This  vessel 
returns  the  venous  blood  from  the  upper  part  of  the  body 
and  opens  into  the  upper  portion  of  the  right  auricle. 

2.  The  opening  of  the  inferior  vena  cava.  This  vessel 
conveys  the  venous  blood  from  the  lower  part  of  the  body 
and  opens  into  the  right  auricle  just  below  the  superior 
vena  cava. 

3.  The  coronary  sinus.  This  is  the  opening  of  the  coro- 
nary vein,  which  returns  the  venous  blood  from  the  sub- 
stance of  the  heart;  this  opening  is  situated  between  that 
of  the  inferior  vena  cava  and  that  in  the  right  auriculo- 
ventricular  septum. 

4.  The  foramina  Thebesii.  These  are  minute  openings 
of  veins  from  the  substance  of  the  heart. 

5.  The  auriculo-ventricular  opening.  This  is  in  the  sep- 
tum separating  the  right  auricle  from  the  left  ventricle. 

Of  these  five  openings,  only  that  of  the  coronary  sinus  is 
provided  with  a  valve,  called  the  coronary  valve. 

Between  the  opening  of  the  inferior  vena  cava  and  the 
auriculo-ventricular  opening  there  is  a  projection  of  endo- 
cardium, called  the  Eustachian  valve;  it  is  large  and  more 
developed  in  foetal  life,  during  which  period  it  serves  to 
direct  the  current  of  the  blood  toward  the  left  auricle. 
During  foetal  life  the  blood  passes  directly  from  the  right 
to  the  left  auricle  through  an  opening  in  the  septum  sepa- 
rating these  cavities;  this  opening,  the  foramen  ovale,  be- 
comes obliterated  at  birth,  but  its  location  remains  visible 
as  a  depression,  called  the  fossa  ovalis,  located  in  the  sur- 


186    LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

face  of  the  septum;  the  lower  border  of  the  fossa  ovalis 
has  a  projection  called  the  annulus  ovalis. 

Between  the  openings  of  the  superior  and  inferior  venae 
cavaB  there  is  a  prominence  called  the  tiiberculum  Loweri; 
it  is  believed  that  this  directs  the  current  of  the  blood  from 
the  venae  cavae  toward  the  auriculo-ventricular  opening. 

The  interior  of  the  main  cavity  of  the  auricle  is  smooth; 
the  surface  of  the  interior  of  the  appendix  auriculae  presents 
minute  muscular  projections  called  the  musculi  pectinati. 

The  right  ventricle  has  a  capacity  of  about  3  ounces;  it 
is  triangular  in  shape,  and  forms  the  interior  of  the  apical 
portion  of  the  right  side  of  the  heart;  its  walls  are  thinner 
than  those  of  the  left  ventricle. 

The  right  ventricle  has  two  openings:  1.  The  opening  of 
the  pulmonary  artery.  2.  The  auriculo-ventricular  open- 
ing. The  opening  of  the  pulmoyiary  artery  is  large  and 
oval.  It  is  situated  in  the  lower  portion  of  the  anterior 
surface  of  the  ventricle  near  the  interventricular  septum. 
This  opening  is  guarded  by  the  semilunar  valve,  consisting 
of  three  semicircular  folds  of  endocardium  which  are  at- 
tached to  the  edge  of  the  opening  by  their  convex  border, 
thus  forming  three  pockets;  their  free  border  is  somewhat 
thick,  and  presents  at  the  centre  a  nodule  called  the  corpus 
Arantii,  from  which  tendinous  fibres  radiate  in  the  sub- 
stance of  the  valve  toward  its  point  of  attachment.  Dur- 
ing the  flow  of  the  blood  from  the  ventricle  into  the  pul- 
monary artery  the  segments  of  the  valve  are  pressed 
against  the  inner  side  of  the  vessel.  The  pulmonary  valve 
serves  to  prevent  a  regurgitation  of  the  blood  from  the 
pulmonary  artery  back  into  the  ventricle.  The  interior  of 
the  artery  presents  a  pouch-like  expansion  behind  the  flaps 
of  the  valve;  if  the  blood  regurgitates  it  fills — this  is  called 
the  sinus  of  Valsalva — and  the  flaps  are  expanded;  the 
triangular  opening  left  in  the  middle,  where  the  free  borders 
of  the  three  flaps  meet,  is  completely  closed  by  the  corpora 
Araiitii,  and  thus  a  regurgitation  is  prevented. 


THE   HEART.  187 

The  auriculo-ventricular  02:)ening  on  the  right  side  is 
guarded  by  a  fold  of  endocardium  which  is  called  the 
tricuspid  valve;  it  consists  of  three  segments,  trapezoidal 
in  form,  which  are  attached  to  the  margin  of  the  auricu- 
lo-ventricular opening  and  also  to  each  other;  from  their 
free  border  and  from  their  ventricular  surface  dehcate 
tendinous  cords,  called  the  chordce  tendinece,  pass  into 
the  ventricular  cavity  and  are  attached  to  the  colum^ice, 
carnecB,  little  muscular  projections  from  the  surface  of  the 
interior  of  the  ventricle;  some  of  these  columnee  carnese 
are  not  attached  to  the  tendinous  cords,  but  are  attached 
their  entire  length,  or  simply  at  one  end,  to  the  surface  of 
the  cavity,  thus  forming  small  ridges  and  loops. 

The  left  am-icle  has  a  capacity  of  about  2^-  ounces;  its 
walls  are  thicker  than  those  of  the  right  auricle,  and  con- 
sequently its  cavity  is  smaller. 

The  left  auricle  also  consists  of  a  main  cavity  and  an 
appendix  auricidce.  The  surface  of  the  former  is  smooth; 
from  that  of  the  appendix  a  small  number  of  musculi  pjec- 
tinati  are  projected.  The  two  auricles  are  separated  by  a 
complete  septum,  called  the  sejjtum  auriculorum. 

The  openings  into  the  left  auricle  are: 

1.  The  openings  of  the  four  pidmonary  veins,  located  in 
the  posterior  walls  of  the  auricle. 

2.  The  auriculo-ventricular  opening,  by  which  the  auri- 
cle communicates  with  the  ventricle. 

There  are  no  valves  in  the  left  auricle.  The  left  ventricle 
has  a  capacity  of  about  3  ounces;  it  is  longer  and  has 
thicker  walls  than  the  left  ventricle,  projects  beyond  it, 
and  forms  the  apex  of  the  heart. 

It  has  two  openings,  namely: 

1.  The  aortic  opening. 

2.  The  auriculo-ventricular  opening.  The  aortic  open- 
ing is  circular  and  is  located  in  front  and  to  the  right  of 
the  auriculo-ventricular  opening.  This  opening  is  guarded 
by  the  semilunar  valve,  which  has  the  same  structure  as 


188     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

the  semilunar  valve  guarding  the  pulmonary  artery.  The 
pouch-like  expansion  behind  the  flaps  of  the  aortic  semi- 
lunar valve  is  deeper;  it  is  also  termed  the  sinus  of  Val- 
salva, or  sinus  aoi^ticus. 

The  auriculo -ventricular  opening  is  located  in  the  au- 
riculo- ventricular  septum;  it  is  guarded  by  a  valve  called 
the  mitral  or  bicuspid  valve.  It  consists  of  two  seg- 
ments attached  to  the  edges  of  the  opening  and  to  each 
other. 

The  anterior  segment,  which  is  placed  between  the  auri- 
culo-ventricular  and  the  aortic  openings,  is  larger  and 
stronger  than  the  posterior.  To  the  free  border  of  the 
segments  and  to  their  ventricular  surface  are  attached  the 
tendinous  cords,  or  chordce  tendinew,  which,  in  the  same 
manner  as  in  the  right  ventricle,  are  attached  to  the  free 
ends  of  the  columnoe  carnece.  The  two  musculi  papilla- 
res  are  more  prominent  and  give  attachment  to  most  of 
the  chordae  tendineae.  The  columnae  carnese  are  most 
abundant  in  the  apical  portion  of  the  ventricle;  they  are 
arranged  similarly  to  those  in  the  right  ventricle.  The 
interventricular  septum  is  thick  toward  the  apex,  but  thin 
and  fibrous  in  the  upper  part. 

The  ivalls  of  the  cavities  of  the  heart  are  composed  of 
involuntary  muscular  fibres;  they  are  so  arranged  that 
their  contraction  causes  a  diminution  of  the  cavities. 

The  muscular  fibres  of  the  auricles  are  separated  from 
those  of  the  ventricles  by  a  fibrous  ring  called  the  amndus 
atrio-ventricularis. 

The  muscular  fibres  of  the  auricles  are  arranged  in  two 
layers:  an  outer  layer,  consisting  of  transverse  fibres  which 
surround  both  auricles,  and  an  inner  layer,  consisting  of 
(«)  longitudinal  and  oblique  fibres  which  are  inserted  ante- 
riorly and  posteriorly  into  the  annulus  atrio-ventricularis; 
(6)  transverse  fibres  which  pass  around  each  auricle  and 
which,  between  the  two,  form  the  interauricular  sep- 
tum; (c)  circular  fibres  which  surround  the  openings  of  the 


THE    HEART.  189 

vessels  into  the  auricles  and  by  their  contraction  close  these 
openings. 

The  muscular  fibres  of  the  ventricles  are  arranged  in  a 
more  complicated  manner.  The  left  ventricle  is  larger 
than  any  of  the  cavities,  and  its  walls  are  thicker.  The 
left  side  of  the  anterior  surface,  the  main  part  of  the 
posterior  surface,  and  the  apex  of  the  heart  form  the  outer 
walls  of  the  left  ventricle. 

The  muscular  walls  of  the  left  ventricle  are  generally 
formed  by  seven  layers  of  spiral  fibres;  these  are  inserted 
in  the  annulus  atrio-ventricularis,  and  wind  around  the 
ventricle,  passing  deeper  and  deeper  into  the  substance  of 
the  wall.  The  fibres  anteriorly  attached  to  the  annulus 
atrio-ventricularis  pass  downward  obliquely  and  around 
the  apex  from  right  to  left;  those  attached  posteriorly  to 
the  annulus  atrio-ventricularis  pass  downward  obliquely 
from  left  to  right  and  wind  around  the  apex.  The  exter- 
nal layers  of  the  spiral  muscular  fibres  pass  around  the 
lower  portion  of  both  ventricles  ;  they  pass  into  the  sub- 
stance of  the  apex  and  finally  terminate  at  the  columnse 
carnese  or  musculi  papillares  of  the  left  ventricle. 

The  deeper  layers  of  these  spiral  muscular  fibres  become 
shorter  and  shorter,  and  surround  only  the  upper  portion 
of  the  left  ventricles.  The  walls  of  the  lower  or  apical  por- 
tion of  this  are  thinner,  as  the  apex  is  formed  only  by  the 
longer  and  more  superficial  muscular  fibres.  The  fibres 
forming  the  walls  of  the  right  ventricle  are  similarly  ar- 
ranged; they  are  shorter,  more  delicate,  and  do  not  enter 
into  the  apex  of  the  heart. 

The  muscular  part  of  the  interventricular  septum  is 
formed  by  the  meeting  of  the  fibres  from  the  right  and 
left  ventricles.  The  blood-supply  reaches  the  substance  of 
the  heart  through  the  right  and  left  coronary  arteries,  two 
vessels  which  arise  from  the  aorta  immediately  above  the 
semilunar  valves. 

The  venous  blood  from  the  substance  of  the  heart  is 


190     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

conveyed  into  the  right  auricle  by  the  coronary  veins  and 
by  the  vena3  cordis  minores. 

Tlie  nerve-supply  to  the  heart  is  from  branches  of  the 
sympathetic  and  pneumogastric  nerves;  several  nerve- 
centres  are  located  in  the  substance  of  the  heart. 

For  the  physical  examination  of  the  heart,  for  the  study 
of  heart-sounds,  and  for  the  diagnosis  of  cardiac  diseases, 
especially  those  of  the  valves,  called  lesions,  it  is  necessary 
to  be  familiar  with  the  location  of  the  various  anatomical 
structures  of  the  heart.  As  you  will  receive  a  practical 
course  in  the  examination  of  the  heart,  I  will  speak  but 
briefly  on  this  subject. 

1.  The  auricles  are  on  a  line  with  the  third  costal  carti- 
lages. The  right  auricle  extends  a  little  beyond  the  right 
border  of  the  sternum.  The  left  auricle  is  covered  by 
the  pulmonary  artery  and  lies  behind  the  cartilage  of  the 
third  left  rib. 

2.  The  ventricles  occupy  a  space  behind  and  to  the  left 
of  the  sternum,  extending  from  the  third  to  the  fifth  inter- 
costal space.  The  right  ventricle  lies  principally  behind 
the  sternum,  while  a  small  portion  of  it  extends  to  the  left 
of  that  bone.  The  left  ventricle  lies  still  more  to  the  left 
of  the  sternum,  extending  to  an  imaginary  line  drawn  ver- 
tically half  an  inch  from  the  left  nipple. 

The  whole  anterior  surface  of  the  heart  is  covered  with 
lung  tissue,  with  the  exception  of  a  small  triangular  por- 
tion of  the  right  ventricle. 

The  relative  positions  of  the  valves  are  as  follows  : 

1.  The  tricuspid  valve  lies  behind  the  middle  of  the  ster- 
num, on  a  line  with  the  sternal  articulation  of  the  fourth  rib. 

2.  The  pulmonary  semilunar  valves  lie  behind  the  arti- 
culation of  the  third  left  rib  with  the  sternum.  The  pul- 
monary artery  rises  from  the  right  ventricle  behind  the 
sternum  near  its  left  border,  and  on  a  level  with  the  ster- 
nal articulation  of  the  third  rib;  it  ascends  and  then  passes 
backward. 


THE   ARTERIES.  191 

3.  The  mitral  valve  lies  behind  the  cost^al  cartilage  of  the 
fourth  left  rib  near  the  border  of  the  sternum. 

4.  The  aortic  semilunar  valves  lie  behind  the  sternum 
near  its  left  border,  and  just  below  the  sterno-costal  arti- 
culation of  the  third  rib.  The  aorta  rises  from  the  left 
ventricle  behind  the  sternum  near  its  left  border,  and  on  a 
level  with  the  third  intercostal  space;  the  aorta  then  passes 
upward  and  to  the  left. 

Hie  Arteries. 

The  blood-vessels  which  convey  the  blood  from  the  heart 
to  the  tissues  are  called  the  arteries.  The  normal  structure 
of  these  vessels  is  an  important  factor  in  the  circulation  of 
the  blood. 

The  walls  of  the  arteries  are  composed  of  three  coats — 
namely;  the  outer  coat,  or  tunica  adventitia ;  Si middle  coat, 
or  tunica  media;  and  an  inner  coat,  or  tunica  intima. 

The  outer  coat,  or  tunica  adventitia,  is  composed  princi- 
pally of  fibrous  tissue  and  contains  elastic  fibres. 

The  middle  coat,  or  tunica  media,  consists  of  non-striated 
muscular  and  elastic  fibres  in  alternating  layers.  In  the 
larger  arteries  the  elastic  element  is  predominant;  in  the 
smaller  arteries  muscular  fibres  are  more  abundant;  while 
in  the  smallest  arteries,  or  arterioles,  the  middle  coat  con- 
tains only  muscular  fibres. 

The  presence  of  elastic  fibres  in  the  external  and  middle 
coats  of  the  arteries  prevents  them  from  collapsing  when 
empty.     On  a  cut  surface  the  lumen  can  be  plainly  seen. 

The  tunica  intima  consists  of  a  delicate  fibrous  mem- 
brane which  contains  elastic  fibres,  and,  in  the  larger  arte- 
ries, muscular  fibres  as  well.  It  has  a  fenestrated  struc- 
ture ;  it  is  therefore  called  the  fenestrated  membrane.  In  the 
smaller  arteries  this  membrane  does  not  present  this  char- 
acteristic structure.  Within  this  is  the  endothelium  which 
lines  all  blood-vessels;  it  consists  of  elongated,  fiat  cells  dis- 
posed in  a  single  layer  upon  a  delicate  basement  membrane. 


192    LECTURES  ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  Capillaries. 

The  capillaries  are  minute,  delicate  blood-vessels  which 
freely  anastomose  in  the  tissues,  through  the  walls  of  which 
the  materials  intended  for  the  nutrition  of  the  tissue  ele- 
ments transude  into  the  interstices  of  the  tissues. 

The  walls  of  the  capillaries  consist  of  a  single  layer  of 
flat  endothelial  cells  which  are  cemented  together  at  their 
sides;  between  these  cells  minute  openings,  called  stomata, 
appear  at  intervals. 

The  Veins. 

The  blood-vessels  which  convey  the  blood  from  the  tis- 
sues to  the  heart  are  called  veins.  They  differ  in  their 
structure  from  the  arteries  in  that  their  lumen  is  larger 
and  their  walls  are  thinner  and  contain  but  few  elastic 
fibres.  The  walls  of  the  veins,  like  those  of  the  arteries, 
consist  of  three  coats. 

The  tunica  adventitia  is  thicker  than  in  arteries  ;  it  is 
composed  mainly  of  fibrous  tissue  containing  some  elastic 
and  muscular  fibres. 

The  tunica  media  is  thinner  than  in  arteries  ;  it  is  com- 
posed of  muscular  fibres  with  few  elastic  fibres. 

The  tunica  intima  has  the  same  structure  as  that  of  the 
arteries  ;  the  larger  veins  also  have  a  fenestrated  mem- 
brane, and  in  some  of  these  the  membrane  between  the 
fenestrated  membrane  and  the  endothelium  contains  some 
elastic  fibres. 

The  larger  veins  in  certain  locations  in  the  body — for 
instance,  those  in  the  neck  and  extremities — are  supplied 
with  valves;  these  are  flaps  projecting  into  the  lumen  of 
the  veins.  They  are  composed  of  fibrous  tissue  containing 
elastic  and  muscular  fibres,  and  a  covering  of  endothelium 
on  both  sides.  These  valves  serve  to  prevent  a  regurgita- 
tion of  the  blood. 

The  venous  blood  from  the  brain  is  returned  through 


THE   VEINS.  193 

channels  formed  by  folds  of  the  dura  mater  lined  with 
endothelium;  such  a  channel  is  termed  a  sinus. 

The  walls  of  the  blood-vessels  are  supplied  with  blood  for 
their  nutrition  by  minute  vessels  which  are  called  the 
vasa  vasorum;  their  structure  is  the  same  as  that  of  other 
blood-vessels. 

The  nerves  supplying  the  walls  of  the  blood-vessels  rise 
from  nerve-centres  and  pass  along  with  other  fibres  in 
large  nerve-trunks  terminating  in  the  muscular  fibres  of 
the  coats  of  the  blood-vessels. 

13 


LECTURE  XXIl. 

THE   heart's   action. 

The  "physiological  activity  of  the  heart  consists  of  a 
rhythmical  contraction  and  relaxation  of  its  auricles  and 
ventricles. 

A  cardiac  pulsation,  or  revolutio  cordis,  consists  of  three 
stages,  namely: 

1.  A  contraction  of  both  auricles. 

2.  A  contraction  of  both  ventricles. 

3.  A  period  of  rest,  during  which  the  auricles  and  ven- 
tricles relax. 

The  events  which  take  place  during  such  a  cardiac  cyclus 
may  be  enumerated  as  follows: 

1.  The  auricles  fill  with  blood  and  dilate,  the  right  auricle 
receiving  the  blood  from  the  superior  and  inferior  venae 
cavae  and  from  the  coronary  veins,  the  left  auricle  receiv- 
ing blood  from  the  pulmonary  veins. 

2.  When  the  auricles  are  completely  filled  they  begin  to 
contract;  the  contraction  begins  at  the  appendices  of  the 
auricles,  by  which  the  blood  is  forced  into  the  main  cavity 
of  the  auricles;  the  contraction  of  their  walls  then  contin- 
ues from  above  toward  the  ventricles.  During  this  stage 
the  openings  of  the  veins  into  the  auricles  are  closed  by  the 
contraction  of  the  circular  fibres  surrounding  these  open- 
ings, and  a  regurgitation  of  blood  into  these  vessels  is  thus 
prevented.  The  pressure  exerted  upon  the  blood  in  the 
auricles  by  the  contraction  of  their  walls  forces  the  blood 
through  the  opening  in  the  auriculo-ventricular  septa  into 
the  ventricles. 

3.  The  ventricles  are  filled  by  the  blood  forced  into  them 


THE   heart's   action.  195 

from  the  auricles;  the  ventricles  dilate,  and  when  filled 
begin  to  contract;  the  segments  of  the  mitral  and  tricuspid 
valves,  owing  to  their  thinness,  float  on  the  blood,  and  are 
so  raised  against  the  auricalo-ventricular  openings,  thus 
preventing  a  regurgitation  of  blood  into  the  auricles  during 
the  contraction  of  the  ventricles.  The  contraction  of  the 
ventricular  walls  upon  the  blood  forces  it  into  the  openings 
of  the  aorta  and  pulmonary  artery. 

4.  The  ventricles  begin  to  relax;  the  blood  forced  into 
the  aorta  and  pulmonary  artery  tends  to  regurgitate,  but  is 
prevented  from  re-entering  the  ventricles  by  the  semilunar 
valves,  which  become  closed  by  the  filling  of  the  sinuses  of 
Valsalva  behind  the  pouches  of  the  flaps  of  the  semilunar 
valves. 

The  simultaneous  contraction  of  the  auricles  is  termed 
the  auricular  systole,  or  systole  atriorum;  that  of  the  ven- 
tricles is  termed  the  ventricular  systole;  and  the  period 
during  w^hich  both  auricles  and  ventricles  are  in  a  state  of 
relaxation  is  termed  the  diastole. 

The  average  duration  of  such  a  cardiac  cyclus  in  the 
healthy  human  adult  is  0.72  second.  If  this  time  is  di- 
vided into  six  equal  parts,  then  the  various  phases  of  a  car- 
diac cyclus  are  as  follows: 

During  periods  1  and  2  the  auricles  are  in  a  state  of  con- 
traction, the  ventricles  in  a  state  of  relaxation. 

During  periods  3,  4,  and  5  the  auricles  are  in  a  state  of 
relaxation,  the  ventricles  in  a  state  of  contraction. 

During  period  6  both  auricles  and  ventricles  are  in  a  state 
of  relaxation. 

From  this  the  time  taken  up  by  each  phase  of  the  cardiac 
cyclus  can  be  easily  calculated. 

The  auricular  contraction  taking  place  during  periods 
1  and  2  takes  up  two-sixths  of  the  whole  time  of  a  cardiac 
cyclus. 

The  auricular  relaxation  taking  place  during  periods 
3,  4,  5,  and  6  takes  up  four-sixths  of  the  whole  time. 


196     LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  ventricular  contraction  taking  place  during  periods 
3,  4,  and  5  takes  up  three-sixths,  and  the  ventricular 
relaxation  taking  place  during  periods  6,  1,  and  2  also 
takes  up  three-sixths  of  the  whole  time  of  a  cardiac  cyclus. 
The  phase  of  diastole — that  is,  when  both  auricles  and  ven- 
tricles are  in  a  state  of  relaxation — takes  place  during 
period  6;  therefore  it  takes  up  one-sixth  of  the  whole  time 
of  the  cardiac  cyclus. 

The  number  of  cardiac  pulsations  per  minute  is  from  G5 
to  75  in  the  average  healthy  human  adult,  180  in  the 
foetus,  150  in  new-born  children,  100  in  the  first  years  of 
infantile  life;  it  then  gradually  diminishes  until  its  normal 
frequency  is  reached;  in  old  age  it  is  slightly  increased. 
The  action  of  the  heart  is  most  regular  in  rhythm  and 
frequency  when  the  body  is  at  rest  and  in  a  horizontal  posi- 
tion. The  frequency  of  the  cardiac  pulsations  is  increased 
by  motion,  excitement,  walking,  and  the  taking  of  nou- 
rishment; it  is  decreased  by  fasting.  Many  pathological 
conditions  increase  or  decrease  the  action  of  the  heart  and 
influence  the  rhythm.  The  physiological  action  of  the 
heart  is  muscular  and  is  ordinarily  dependent  upon  proper 
nerve  influence,  and  it  is  therefore  necessary  to  study  and 
understand  the  nervous  system  of  the  heart. 

The  heart  receives  nerve-fibres  from  the  pneumogastric 
and  sympathetic  nerves  through  the  cardiac  plexus;  besides 
these  there  are  located  in  the  substance  of  the  heart  itself 
the  so-called  inherent  ganglia. 

The  inherent  ganglia  are  small  ganglionic  masses  of 
nerve  substances;  they  are  located  principally  in  the  inter- 
auricular  and  auriculo-ventricular  septa.  These  ganglia 
communicate  with  each  other  by  delicate  fibrillar  processes, 
and  numerous  fibres  from  these  ganglia  are  distributed 
throughout  the  substance  of  the  heart,  terminating  in  its 
muscular  fibres.     Remak  first  described  these  ganglia. 

The  experiments  of  Stannius  demonstrated  that  these 
ganglia  are  motor  ganglia  and  that  they  act  automatically. 


THE    heart's   action.  197 

When  the  nerve-fibres  which  are  distributed  to  the  heart 
from  the  cardiac  plexus  are  cut  the  heart  will  continue  to 
beat;  this  shows  that  the  cause  of  the  heart's  action  is  lo- 
cated in  the  substance  of  the  organ,  and  it  also  shows  that 
the  activity  of  the  centres  or  ganglia  in  the  heart  is  not 
dependent  upon  external  nerve  influence. 

The  largest  and  most  important  automatic  motor  gan- 
glion of  the  heart  is  located  in  the  interauricular  septum, 
and  from  this  the  stimulus  is  transmitted  to  the  others; 
this  explains  why  the  rhythmical  contractions  of  the  car- 
diac muscle  begin  in  the  auricles. 

The  cardiac  plexus  is  formed  by  branches  from  the 
pneumogastric  and  sympathetic  nerves.  The  plexus  is 
located  near  the  base  of  the  heart  and  is  divided  into  a 
deep  and  a  superficial  portion.  The  deep  cardiac  plexus  is 
situated  between  the  trachea  and  the  aorta;  its  branches 
form  the  posterior  coronary  plexus,  from  which  fibres  are 
distributed  to  the  posterior  wall  of  the  heart.  The  super- 
ficial cardiac  plexus  is  situated  in  the  concavity  of  the  arch 
of  the  aorta;  its  branches  form  the  anterior  coronary 
plexus,  from  which  fibres  are  distributed  to  the  anterior 
wall  of  the  heart. 

The  cardiac  plexus  contains  vasomotor,  sensory,  inhibi- 
tory, and  acceleratory  fibres,  which  are  distributed  to  the 
heart. 

The  iyihihitory  fibres  rise  from  a  centre  which  is  located 
in  the  medulla  oblongata  in  the  apex  of  the  calamus  scrip- 
torius;  an  irritation  of  this  centre  causes  a  decrease  in  the 
cardiac  contractions.  The  inhibitory  fibres  pass  in  the 
pneumogastric  nerve  to  the  cardiac  plexus.  Section  of  the 
pneumogastric  nerves  causes  an  accelerated  heart-action. 

The  acceleratory  fibres  rise  from  centres  which  are  lo- 
cated in  the  brain  and  upper  portion  of  the  spinal  cord. 
Irritation  of  the  medulla  oblongata  or  upper  cervical  portion 
of  the  spinal  cord  causes  an  accelerated  heart-action. 
From   their   centres   these   accelerating  nerve-fibres  pass 


198     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

down  in  the  spinal  cord,  leave  the  canal  with  the  cervical 
and  upper  dorsal  nerves,  and  these  communicate  with  the 
last  cervical  and  first  dorsal  ganglia  of  the  sympathetic  nerve, 
from  which  branches  are  distributed  to  the  cardiac  plexus 

The  heart  is  evidently  supplied  with  sensory  nerve-fibres; 
this  is  shown  by  the  pains  experienced  in  certain  heart- 
diseases.  These  fibres  are  probably  derived  from  the  pneu- 
mogastric. 

From  this  description  of  the  nervous  mechanism  of  the 
heart  we  learn,  therefore,  that  the  motions  of  the  organ 
are  caused  by  the  action  of  the  inherent  automatic  motor 
ganglia,  and  that  the  rhythm  of  these  motions  is  regulated 
by  the  infiuence  of  nerves  which  are  connected  with  cen- 
tres in  the  brain  and  medulla.  The  stimulus  for  the  nor- 
mal activity  of  these  centres  is  the  same  as  that  for  all 
nerve-centres — namely,  a  proper  exchange  of  the  gases  in 
the  blood. 

The  rhythmical  motions  of  the  heart  produce  certain 
changes  in  its  position  and  in  its  form. 

The  heart  is  attached  by  its  base  to  the  large  vessels, 
consequently  only  its  body  and  apex  are  movable;  changes 
in  its  position  must  therefore  be  coincident  with  the  mo- 
tions of  its  apical  or  ventricular  portion.  During  the  ven- 
tricular systole  the  main  part  of  the  heart  rotates  on  its 
axis  forward  and  to  the  right,  the  apex  twists  forward  to 
the  right  and  upward  ;  this  peculiar  motion  is  due  to  the 
peculiar  anatomical  arrangement  of  the  ventricular  fibres. 
During  the  relaxation  of  the  ventricles  the  reverse  changes 
in  the  position  of  the  heart  take  place. 

The  changes  in  the  form  of  the  heart  during  its  motions 
may  be  described  as  follows:  During  its  contraction  there 
is  a  shortening  of  the  longitudinal  and  a  narrowing  of  the 
transverse  diameter  anteriorly,  while  posteriorly  the  longi- 
tudinal diameter  is  lengthened;  these  changes  are  caused 
by  the  muscular  fibres  of  the  ventricles  and  the  tilting  for- 
ward of  the  apex  of  the  heart.     This  forward  motion  of 


THE   HEART'S  ACTION.  199 

the  heart's  apex  can  be  easily  felt  with  the  hand;  it  is 
also  perceptible  to  the  eye  by  the  elevation  of  the  chest- 
wall  in  the  fifth  intercostal  space  on  the  left  side  of  the 
sternum.  This  phenomenon  produced  by  the  cardiac  mo- 
tions is  called  the  axjex  heat,  the  cardiac  impulse,  or  ictus 
cordis;  it  is  synchronous  with  the  ventricular  systole. 
During  activity  there  are  produced  certain  sounds  which 
are  called  the  heart-sounds;  they  are  two  in  number  and 
can  be  heard  by  placing  the  ear  over  the  cardiac  region; 
they  are  known  as  the ^rs^  and  second  heart-sounds.  The 
first  sound  is  muscular,  produced  by  the  contraction  of  the 
fibres  of  the  ventricles;  it  is  strengthened  by  the  vibrations 
of  the  chordae  tendinese  and  by  the  sound  produced  by  the 
closing  of  the  mitral  and  tricuspid  valves.  The  first  heart- 
sound  is  dull,  deep,  and  long;  it  is  most  distinctly  heard 
over  the  apex  in  the  fifth  left  intercostal  space. 

The  second  heart-sound  is  produced  by  the  closing  of  the 
semilunar  valves  of  the  aorta  and  pulmonary  artery,  and 
is  heard  directly  over  these  valves.  It  is  short,  clear,  and 
high-pitched,  and  immediately  follows  the  first  heart- 
sound.  Between  the  first  and  second  sounds  there  is  a 
period  of  silence. 

The  normal  action  of  the  heart  and  the  phenomena  ac- 
companying it  are  often  altered  in  many  pathological  con- 
ditions. The  rhythm  of  the  pulsations,  their  strength,  and 
the  periods  of  the  various  phases  of  a  cardiac  pulsation 
may  be  altered.  The  cardiac  impulse,  or  apex-beat ,  may 
be  abnormally  strong  or  weak,  or  it  may  be  perceptible  in 
an  abnormal  location.  The  sounds  of  the  heart  may  be 
changed  in  their  character.  In  certain  valvular  diseases 
abnormal  sounds  are  produced  within  the  heart ;  they  are 
described  as  cardiac  murmurs. 

The  circulation  of  the  blood  is  maintained  principally  by 
the  action  of  the  heart,  by  which  the  necessary  variations 
of  the  blood-pressure  in  the  different  parts  of  the  circu- 
latory system  are  maintained. 


200     LECTURES   OX    HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

The  hlood-pressure  is  the  pressure  which  the  column  of 
blood  exerts  perpendicularly  upon  the  walls  of  the  vessel 
which  it  fills.  If  the  blood-pressure  were  equal  in  all  parts 
of  the  circulatory  system  the  blood  would  not  circulate; 
but,  as  the  pressure  is  greater  in  one  part  than  in  another, 
the  blood  will  flow  in  the  direction  where  it  finds  the  least 
resistance.  In  the  animal  body  these  necessary  variations- 
of  the  blood-pressure  are  maintained  by  the  action  of  the 
heart.  During  each  diastole  the  auricles  draw  into  them- 
selves a  quantity  of  blood  from  the  venous  circulation,  and 
at  each  systole  the  ventricles  force  a  quantity  of  blood  into- 
the  arterial  circulation.  At  each  cardiac  pulsation,  there- 
fore, the  blood-pressure  is  decreased  in  the  venous  system 
and  increased  in  the  arterial,  and  the  result  is  that  the  blood 
circulates  from  the  arterial  to  the  venous  side.  The  blood- 
pressure  in  the  vascular  system  is  furthermore  regulated 
by  the  properties  of  the  walls  of  the  blood-vessels  and  by 
other  auxiliary  factors,  such  as  muscular  pressure,  respira- 
tory movements,  etc. 

To  measure  the  blood-pressure  a  glass  canula  is  intro- 
duced into  the  blood-vessel ;  the  canula  is  connected  by 
means  of  a  rubber  tube  with  a  mercurial  manometer  ;  the 
connecting  tube  is  filled  with  a  saline  solution  ;  the  pres- 
sure of  the  blood  in  the  vessel  is  transmitted  by  the  saline 
solution  to  the  column  of  mercury  in  the  manometer  and 
causes  a  rise  of  the  mercury  in  the  graduated  tube.  The 
height  of  the  column  of  mercury  multiplied  by  its  trans- 
verse diameter  is  the  weight  of  the  mercury  raised  by  the 
blood-pressure. 

Experiments  have  shown  that  the  blood-pressure  in  the 
aorta  is  about  4  pounds  and  -t  ounces,  whereas  the  blood- 
pressure  in  the  radial  artery  is  only  about  4  di'achms. 

The  blood-pressure  is  greatest  in  the  left  ventricle  of  the 
heart ;  it  is  greater  in  the  aorta  and  in  the  larger  arteries 
than  in  the  smaller.  It  diminishes  in  the  arteries  as  the 
sectional  area  of  their  calibre  increases. 


THE  heart's  action.  201 

The  blood-pressure  in  the  arteries  is  increased  : 

1.  By  a  forcible  and  increased  heart-action, 

2.  By  an  increase  of  blood  in  the  arteries. 

3.  By  a  decrease  in  the  calibre  of  the  lumen  of  the  arte- 
ries; as,  for  instance,  by  muscular  pressure,  or  by  a  con- 
traction of  the  muscular  fibres  of  the  arteries. 

4.  By  expiration,  since  this  increases  the  intrathoracic 
pressure. 

5.  By  an  increase  in  the  resistance  which  the  current  of 
the  blood  has  to  overcome. 

The  blood-pressure  in  the  arteries  is  decreased: 

1.  By  a  weak  heart-action. 

2.  By  a  decrease  in  the  quantity  of  the  blood  in  the  arte- 
rial system. 

3.  By  the  increase  in  the  lumen  of  the  arteries. 

4.  By  the  diminution  of  the  resistance  presenting  itself 
to  the  current  of  blood. 

5.  By  inspiration,  since  this  decreases  the  intrathoracic 
pressure. 

The  blood-pressure  in  the  capillaries  cannot  be  directly 
measured,  owing  to  the  minute  calibre  of  these  vessels;  it 
has  been  estimated  that  the  pressure  of  blood  in  them  is 
about  20  to  60  milligrammes.  This  pressure  is  increased: 
1.  By  an  increase  of  the  blood-pressure  in  the  arterial  sys- 
tem. 2.  By  obstructions  in  the  venous  system.  The  re- 
verse conditions  decrease  the  blood-pressure  in  the  capil- 
lary system. 

The  blood-pressure  in  the  veins  is  much  less  than  that  in 
the  arteries;  it  is  very  inconstant.  It  is  greater  in  the 
smaUer  veins,  and  decreases  as  the  lumen  of  the  vessels 
increases. 

The  blood-pressure  in  the  veins  is  principally  influenced 
by: 

1.  The  arterial  and  capillary  blood-pressure. 

2.  The  quantity  of  blood  in  the  veins. 

3.  The  position  of  the  body. 


202    LECTURES   ON    HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  variations  in  the  blood-pressure  in  the  system  are 
recorded  by  means  of  an  instrument  which  is  called  the 
kymograph.  It  consists  of  a  U-shaped  glass  tube  partially 
filled  with  mercury;  one  end  of  this  tube  is  connected  by  a 
rubber  tube  with  a  glass  canula  which  is  inserted  in  the 
blood-vessel  parallel  with  its  long  axis;  the  connecting  tube 
is  filled  with  a  saline  solution,  which  transmits  the  pressure 
of  the  blood  to  the  column  of  mercury  in  the  U-shaped 
tube,  and  any  changes  in  the  blood-pressure  are  indicated 
by  a  rising  or  sinking  of  the  column  of  mercury  in  the  free 
end. 

These  variations  are  recorded  permanently  upon  a  re- 
volving strip  of  paper  by  a  piston  which  floats  upon  the 
column  of  mercury  and  which  is  connected  with  a  pencil. 
A  tracing  indicating  the  blood-pressure  in  a  vessel  shows 
various  elevations  and  depressions.  The  more  perpendicu- 
lar elevations  and  sudden  descending  lines  indicate  the  in- 
crease and  decrease  during  the  systole  and  diastole  of  the 
heart;  the  more  wavy  lines  in  the  tracing  indicate  the  va- 
riations of  the  blood-pressure  caused  by  the  respiratory 
movements. 

Inspiration  causes  an  increase  in  the  thoracic  cavity  by 
an  expansion  of  its  walls  and  a  descent  of  the  diaphragm; 
the  pressure  upon  the  heart  and  interthoracic  viscera  is 
diminished;  the  heart  expands  and  aspirates  a  quantity  of 
blood  from  the  venous  circulation,  thus  decreasing  the 
blood  pressure  in  the  vessels.  Expiration  causes  a  decrease 
in  the  thoracic  cavity;  its  walls  are  retracted,  the  diaphragm 
raised,  and  thus  the  intrathoracic  pressure  upon  the  heart 
and  blood-vessels  is  increased;  moreover  the  contraction  of 
the  heart  forces  a  quantity  of  blood  into  the  arterial  sys- 
tem, thus  increasing  the  blood-pressure  in  the  vessels. 

The  blood  in  the  human  body  circulates  from  the  left 
side  of  the  heart  into  the  arterial  system;  by  circulating  in 
the  capillaries  the  blood  is  freely  distributed  to  all  parts  of 
the  tissues,  and  is  returned  from  them  as  venous  blood  into 


THE  heart's  action.  203 

the  right  side  of  the  heart.  The  right  auricle  receives  ven- 
ous blood  from  the  superior  and  inferior  venae  cavge  and 
from  the  veins  of  the  heart  substance;  from  the  right 
auricle  the  blood  passes  through  the  right  auriculo-ventri- 
cular  opening  into  the  right  ventricle;  from  this  the  ven- 
ous blood  is  conveyed  by  the  pulmonary  artery  through 
the  lungs,  where  it  becomes  oxygenized,  and  is  returned 
as  arterial  blood  by  the  pulmonary  veins  into  the  left 
auricle;  from  this  the  blood  passes  through  the  left  auri- 
culo-ventricular  opening  into  the  left  ventricle,  and  thence 
into  the  aorta  and  arterial  system. 

The  factors  of  the  circulation  of  the  blood  through  the 
heart  are  as  follows:  The  flow  of  the  blood  from  the  su- 
perior and  inferior  venae  cavae  and  from  the  cardiac  v^ins 
into  the  right  auricle,  and  the  flow  of  the  blood  from  the 
pulmonary  veins  into  the  left  auricle,  is  caused:  1.  By  the 
force  of  the  blood  in  these  vessels — that  is,  the  force  from 
behind. 

2.  The  suction  in  front  is  caused  by  the  vacuum  pro- 
duced in  the  auricles  by  their  dilatation.  From  the  auricles 
into  the  ventricles,  and  from  these  into  the  arterial  system, 
the  blood  is  forced  by  the  contraction  of  the  muscular  walls 
of  the  heart. 

The  factors  of  the  circulation  of  the  blood  in  the  arteries 
are: 

1.  The  ventricular  contractions  of  the  heart. 

2.  The  elasticity  of  the  coats  of  the  arteries. 

At  each  ventricular  contraction  the  heart  forces  about 
150  to  180  grammes  of  blood  into  the  arteries,  thus  sud- 
denly increasing  the  blood-pressure  in  these  vessels;  owing 
to  the  elasticity  of  the  walls  of  the  arteries  their  distension 
is  partially  neutralized,  and  the  reaction  of  the  elastic  walls 
upon  the  columns  of  blood  causes  a  flow  in  the  direction 
where  it  finds  the  least  resistance — namely,  toward  the 
veins;  a  regurgitation  of  the  blood  into  the  heart  is  pre- 
vented by  the  closing  of  the  semilunar  valves.     The  flow 


204      LECTURES    ON    HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

of  the  blood  in  the  arteries  becomes  gradually  more  contin- 
ous  as  their  calibre  decreases. 

The  flow  of  the  blood  in  the  capillaries  is  from  the  arte- 
rial to  the  venous  side,  owing  to  the  greater  pressure  in  the 
former.  The  flow  of  the  blood  in  the  capillaries  is  contin- 
uous and  regular.  In  the  capillaries  the  current  of  blood 
meets  the  greatest  resistance,  owing  to  the  minute  calibre 
and  many  ramifications  of  these  vessels,  and  owing  to  the 
great  friction  the  blood  is  subjected  to  by  its  contact  with 
the  large  amount  of  surface  presented  in  the  walls  of  the 
capillaries. 

The  factors  which  cause  and  influence  the  flow  of  the 
blood  in  the  veins  may  be  enumerated  as  follows: 

1.  The  pressure  of  the  blood  from  behind, 

2.  The  relaxation  of  the  vessels  in  front,  produced  by  the 
aspiration  of  blood  into  the  auricles  of  the  heart. 

3.  The  activity  of  the  muscular  fibres  of  the  walls  of  the 
veins. 

4.  The  valves  in  the  interior  of  the  veins. 

5.  The  gravity  of  the  blood. 

6.  The  pressure  of  muscles. 

7.  The  respiratory  movements. 

The  rapidity  with  which  the  blood  circulates  in  the  vari- 
ous parts  of  the  system  has  been  observed  and  studied  by 
experiments,  with  the  following  results:  It  is  greatest  in 
the  arteries,  and  diminishes  as  the  blood  flows  from  the 
heart  to  the  veins  and  again  to  the  heart.  The  rapidity  of 
the  flow  is  greater  in  the  large  than  in  the  smaller  arteries, 
and  it  diminishes  proportionally  as  the  sectional  area  of 
the  arteries  at  a  given  point  increases.  From  experiments 
it  has  been  estimated  that  the  blood  in  the  aorta  flows 
at  the  rate  of  400  millimetres  a  second,  whereas  in  the 
capillaries  it  flows  at  a  rate  of  only  0.8  millimetre  per 
second.  In  the  veins  the  rapidity  of  the  flow  of  the  blood 
is  inconstant ;  it  diminishes  in  proportion  as  the  calibre  of 
the  veins  increases. 


THE  heart's  action.  205 

The  time  which  is  required  for  the  blood  to  pass  once 
through  the  whole  circulatory  system  has  been  estimated 
to  be  23.2  seconds  at  the  rate  of  72  cardiac  pulsations  per 
minute. 

The  physiological  condition  of  the  walls  of  the  blood- 
vessels must  also  be  considered  an  important  factor  in  the 
circulation  of  the  blood.  Normally  the  walls  of  the  blood- 
vessels are  maintained  in  a  constant  state  of  partial  con- 
traction, a  condition  which  is  called  the  tonus  of  the  blood- 
vessels. It  depends  upon  nerve  influence;  it  is  therefore 
necessary  to  study  the  nervous  system  of  the  blood-vessels. 
The  walls  of  all  blood-vessels  are  supplied  with  nerve-fibres 
which  arise  in  nerve-centres  and  terminate  in  the  muscular 
fibres  of  the  walls.  These  nerve-fibres  are  divided  into 
vasomotor^  or  vasoconstrictor  and  vasodilator  fibres  ;  the 
names  indicate  their  functions.  The  centres  from  which 
these  fibres  arise  are  called  vasomotor  and  vasodilator 
nerve-centres.  In  the  walls  of  the  blood-vessels  there  are 
located  the  so-called  vascular  nerve-centres. 

The  vasomotor  or  vasoconstrictor  nerve- fibres  arise 
from  nerve-centres,  one  of  which  is  located  in  each  side  of 
the  medulla  oblongata;  from  these  the  fibres  pass  down  in 
the  lateral  columns  of  the  cord  and  leave  the  spinal  canal 
together  with  the  anterior  roots  of  the  spinal  nerves,  and 
these  unite  with  spinal,  cranial,  and  sympathetic  nerve- 
trunks  and  are  distributed  from  these  to  the  walls  of  the 
blood-vessels.  The  trunks  of  the  cervical,  sympathetic,  of 
the  splanchnic,  and  of  many  spinal  nerves — as,  for  instance, 
the  ischiatic  nerve — contain  vasomotor  fibres  in  abun- 
dance. Section  of  such  nerve-trunks  causes  a  dilatation, 
stimulation  of  the  same,  a  contraction  of  the  vessels  in  the 
regions  supplied  by  these  nerves. 

The  vasomotor  centres  from  which  these  fibres  arise  are 
automatic ;  their  normal  activity  is  not  due  to  peripheral 
stimuli.  Under  certain  circumstances  these  centres  are 
abnormally  irritated  by  stimuli  received  through  periphe- 


206     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

ral  sensory  nerves.  Certain  psychical  events,  such  as 
shock,  fright,  fear,  etc.,  cause  a  sudden  paleness,  resulting 
from  a  contraction  of  the  blood-vessels;  this  is  then  a  reflex 
act  resulting  from  an  abnormal  irritation  of  the  vasomotor 
centres  by  a  stimulus  received  through  sensory  nerves. 

The  vasodilator  fibres  arise  from  centres  the  exact  loca- 
tion of  which  has  not  yet  been  demonstrated.  The  fibres 
are,  like  the  vasomotor  fibres,  contained  in  sympathetic, 
cranial,  and  spinal  nerve-trunks,  and  terminate  in  the  mus- 
cular fibres  of  the  walls  of  the  blood-vessels. 

The  influence  of  these  nerve-fibres  can  be  compared  to 
that  of  the  inhibitory  fibres  of  the  pneumogastric  nerve  on 
the  heart.  It  has  been  observed  that  certain  events  pro- 
duce a  sudden  dilatation  of  the  blood-vessels  ;  this  must  be 
considered  as  an  abnormal  irritation  of  the  vasodilator 
centres  by  a  stimulus  received  through  peripheral  sensory 
nerves;  blushing  must  be  considered  a  reflex  act  so  pro- 
duced. 

The  vascular  centres  located  in  the  walls  of  the  blood- 
vessels evidently  influence  their  tonus.  It  is  a  well-known 
fact  that  cold  produces  a  contraction,  warmth  a  dilatation, 
of  the  blood-vessels  ;  this  may  probably  be  a  reflex  act 
caused  by  the  thermal  influence  on  the  peripheral  sensory 
nerves,  but  observations  tend  to  show  that  the  effect  pro- 
duced is  mainly  due  to  an  abnormal  stimulation  of  the 
vascular  centres  in  the  walls  of  the  blood-vessels. 


LECTUEE  XXril. 

THE   PULSE   AND   THE   TECHNIQUE   OF   ITS   EXAMINATION, 

Before  finishing  the  subject  of  the  blood  circulation  I 
will  speak  of  the  method  which  is  generally  employed  in 
studying  the.  strength  and  rhythm  of  the  cardiac  pulsa- 
tions and  the  condition  of  the  blood-vessels;  this  is  the 
examination  of  the  pulse. 

The  sudden  distension  of  the  arterial  walls  which  is 
caused  by  each  ventricular  systole,  and  the  reaction  of  the 
elastic  arterial  coat  upon  the  column  of  the  blood,  is  per- 
ceptible both  to  the  eye  and  to  the  touch  as  a  sudden  ele- 
vation or  distension  and  a  more  gradual  relaxation  of  the 
arterial  walls;  this  is  called  the  pulse,  and  is  more  pro- 
nounced in  the  larger  than  in  the  smaller  arteries.  The 
pulse  indicates  the  strength  and  rhythm  of  the  cardiac 
pulsations  and  the  condition  of  the  arterial  walls.  These 
principal  factors  of  the  circulation  are  often  influenced  by 
pathological  conditions;  the  pulse,  therefore,  is  a  very  im- 
portant aid  in  physical  examination.  Even  ancient  writers 
like  Hippocrates,  Herophilus,  and  Galenus  mentioned  in 
their  writings  the  importance  of  pulse  examination  in  dis- 
ease. In  order  to  study  the  pulse  in  disease  it  is  necessary 
to  be  fully  familiar  with  the  character  of  the  healthy  pulse, 
and,  furthermore,  with  the  technique  of  pulse  examination. 

In  examining  the  pulse  the  examiner's  index  and  mid- 
dle fingers  are  placed  with  a  gentle,  even  pressure  upon 
the  radial  artery  at  the  lower  end  of  the  radius.  The 
examiner  must  observe  the  frequency,  the  strength,  and 
the  rhythm  of  the  pulsations  and  the  character  of  the  ar- 
terial walls. 


208      LECTURES    ON    HUMAN   PHYSIOLOGY"   AND    HISTOLOGY. 

1.  l^he  frequency  of  the  pulse.  In  the  healthy  adult  man 
the  pulse  beats  about  72  times,  in  women  about  SO  times 
per  minute.  The  pulse  of  a  new-born  infant  beats  from 
120  to  150  times  per  minute:  it  then  decreases  in  frequency 
until  about  the  twentieth  year;  from  that  time  until  the 
fiftieth  or  sixtieth  year  it  remains  the  same;  in  old  age  its 
frequency  again  increases.  The  frequency  of  the  pulse  in 
health  is  influenced  by  various  conditions;  it  is  most  regu- 
lar when  the  body  is  at  rest  and  in  a  horizontal  position. 
The  pulse  is  more  frequent  when  the  body  is  erect;  its 
frequency  is  increased  by  muscular  activity,  excitement, 
mental  or  sexual  irritation,  and  often  by  the  taking  of 
food;  it  is  decreased  by  fasting.  Variations  in  the  atmo- 
spheric pressure  influence  the  frequency  of  the  pulse;  this 
is  increased  when  the  atmospheric  pressure  is  decreased, 
and  vice  versa.  The  frequency  is  much  altered  by  patho- 
logical conditions.  It  is  increased  in  all  febrile  conditions, 
and  in  many  chronic  and  wasting  diseases.  Its  frequency 
is  decreased  in  many  cerebral  diseases.  Cardiac  lesions 
also  influence  the  frequency  of  the  pulse.  An  abnormally 
quick  pulse  is  termed  pulsus  frequeus,  and  an  abnormally 
slow  pulse  a  p«tZ.S'^;s  rarus.  In  many  pathological  condi- 
tions the  frequency  of  the  pulse  is  increased  to  130  and  150 
beats  per  minute,  and  in  a  condition  termed  pyknocarclia 
a  pulse-frequency  of  250  beats  per  minute  has  been  ob- 
served. Abnormal  decrease  of  the  pulse-frequency  is  often 
an  alarming  symptom  of  disease;  in  a  condition  termed 
spaniocardia  the  pulse  sometimes  only  beats  40  times  per 
minute.  Many  diTigs  influence  the  pulse- frequency — for 
instance,  digitalis  decreases,  while  other  drugs,  like  atro- 
pine, belladonna,  strychnine,  increase  the  frequency  It  is 
therefore  necessary,  when  examining  the  pulse  as  to  its 
frequency,  to  consider  the  many  conditions  which  influ- 
ence it. 

2.  The  rhythm  of  the  pulse.  In  the  normal  pulse  the 
beats  follow  at  regular  intervals.     This  rhythm  is  altered 


THE   PULSE   AND    THE   TECHNIQUE    OF   ITS   EXAMINATION.   209 

in  many  pathological  conditions,  and  often  indicates  car- 
diac lesions.  The  rhythm  of  the  pulsations  may  be  so 
altered  that  their  regularity  is  interrupted  by  the  skipping 
of  a  beat — the  pulse  is  then  called  a  loulsus  intermittens;  or 
the  regularity  is  interrupted  by  an  intercurrent  beat,  and 
the  pulse  is  then  called  intercurrent. 

3.  The  strength  of  the  pulse  is  often  altered,  and  is  indi- 
cative of  changes  in  the  strength  of  the  cardiac  pulsations, 
and  also  of  abnormal  conditious  of  the  walls  of  the  blood- 
vessels. The  pulse  may  be  abnormally  strong  or  hard,  or 
weak  and  soft;  the  hardness  and  softness  of  the  pulse  indi- 
cate changes  in  the  structure  of  the  walls.  The  pulse  may 
be  large  and  full,  or  it  may  be  small;  these  alterations  are 
indicative  of  the  quantity  of  blood  in  the  vessels. 

4.  The  character  of  the  walls  of  the  blood-vessels  can  be 
ascertained  by  studyiug  the  pulse;  this  is  sometimes  small 
and  hard,  or  soft  and  wiry,  or  quick  and  jerky;  these  dif- 
ferences are  principally  due  to  changes  in  the  tonus  of  the 
vessels,  or  to  pathological  changes  in  their  walls,  such  as 
impaired  elasticity  or  abnormal  increase  of  fibrous  tissue. 

In  patients  with  high  fevers  the  frequency  of  the  pulse 
is  generally  proportionally  increased,  and  often  has  a  pe- 
culiarity which  is  known  as  clicrotism.  In  this  condition 
each  pulsation  consists  of  two  beats;  the  first  is  large  and 
is  suddenly  followed  by  a  smaller  beat.  This  peculiarity  is 
produced  by  the  frequent  but  weak  ventricular  systole  and 
the  consequently  more  forcible  secondary  distension  of  the 
arterial  walls,  produced  by  a  rebounding  of  the  blood  from 
the  closed  semilunar  aortic  valves. 

Many  instruments  have  been  devised  for  a  more  definite 
and  exact  study  of  the  pulse  and  for  the  recording  of  its 
conditions.  The  instrument  employed  for  this  purpose  is 
the  sphygmograph,  of  w^hich  several  kinds,  differing  in 
their  structure,  exist. 

I  will  describe  the  sphygmograph  devised  by  Marey,  of 
Paris,  in  1860,  which  instrumeut  has  been  greatly  improved 

14 


210     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

since  that  time.  It  consists  of  a  metallic  frame  with  an 
arrangement  for  its  adjustment  to  the  arm  of  the  patient 
by  means  of  straps  ;  to  the  frame  is  attached  a  spring,  and 
to  the  free  end  of  this  a  rounded  button,  which  by  the 
force  of  the  spring  is  slightly  pressed  upon  the  blood- 
vessel, generally  the  radial  artery ;  this  button  conse- 
quently follows  the  up-and-down  motions  of  the  walls  of 
the  blood-vessels.  With  the  button  is  connected  a  rod 
which  transmits  its  movements  to  a  lever  ;  at  the  free  end 
of  this  is  fastened  a  pen  or  pencil  which  records  the  move- 
ments of  the  button,  transmitted  by  the  lever  upon  a  long- 
strip  of  paper  ;  this  is  fastened  to  a  vertical  plate  which  is 
moved  by  clockwork,  on  a  rail,  at  a  uniform  rate.  The 
slip  of  paper  passes  the  point  where  the  recording  pen  or 
pencil  moves  up  and  down  in  ten  seconds,  and  in  that  time 
the  pencil  marks  on  the  paper  a  tracing  which  is  known  as 
the  sphygmogram.  A  sphygmographic  tracing  consists  of 
a  wavy  line,  the  ascending  portions  of  which  indicate  the 
sudden  distension  of  the  arterial  walls  by  the  ventricular 
systole  ;  the  descending  portions  are  more  wavy,  showing 
generally  several  secondary  elevations,  which  indicate  the 
gradual  relaxation  of  the  arterial  walls  during  the  cardiac 
systole.  The  angle  or  apex  formed  at  the  point  where  the 
ascent  terminates  and  the  descent  begins  indicates  the 
point  of  the  maximal  distension  of  the  arterial  walls.  The 
descending  portions  in  the  sphygmographic  tracing  have,  as 
I  have,  stated  above,  several  secondary  elevations.  The  first 
one  of  these  is  in  the  upper  third  and  is  the  most  promi- 
nent one  ;it  is  produced  by  the  blood  rebounding  from  the 
closed  semilunar  aortic  valves,  which  causes  a  secondary 
distension  of  the  arterial  walls.  The  other  minor  eleva- 
tions in  the  descending  portions  are  produced  by  the 
vibrations  of  the  elastic  arterial  walls.  A  careful  inspec- 
tion of  the  sphygmogram  will  show  that  the  whole  trac- 
ing has  a  wavy  appearance,  produced  by  the  increase 
and  decrease  of  the  blood-pressure  during  the  respiratory 


THE    PULSE    AND    THE    TECHNIQUE    OF    ITS   EXAMINATION.    211 

niOYements.     The  sphygmogram   therefore   indicates   the 
following : 

1.  The  number  of  cardiac  pulsations  in  the  time  of  ten 
seconds.  In  the  healthy  adult  the  pulse  beats  from  72  to  80 
times  a  minute,  or  about  12  times  in  ten  seconds.  On  the 
sphygmogram  each  pulsation  is  represented  by  an  ascend- 
ing line,  a  summit,  and  a  descending  line.  A  smaller  num- 
ber than  12  of  such  figures  in  the  sphygmogram  would 
therefore  indicate  a  decrease,  a  larger  number  an  increase, 
in  the  cardiac  pulsations. 

2.  The  force  of  the  ventricular  systole  is  indicated  by  the 
sudden  ascent  and  height  of  the  ascending  portion  ;  nor- 
mally this  line  ascends  very  slightly  obliquely,  almost  ver- 
tically. 

3.  The  condition  of  the  elastic  walls,  indicated  by  the 
oblique  descent  and  secondary  elevations  of  the  descend- 
ing line.  A  slow  or  sudden  descent  or  absence  of  second- 
ary elevations  indicates  a  lack  of  elasticity  of  the  arterial 
walls. 

4.  The  rhythm  of  the  cardiac  pulsations  is  indicated  by 
the  regularity  of  the  ascending  and  descending  lines  in  the 
sphygmogram. 

The  sphygmograph  is  principally  employed  as  an  aid  in 
the  diagnosis  of  diseased  conditions  of  the  blood-vessels 
and  valvular  lesions  of  the  heart. 

The  most  frequent  pathological  condition  of  the  arterial 
waUs  is  a  loss  of  their  elasticity.  In  the  sphygmographic 
tracing  this  is  indicated  by  the  sudden  secondary  elevation 
which  is  seen  high  in  the  descending  hue,  and  the  slight 
minor  secondary  elevations. 

The  more  frequent  valvular  lesions,  in  the  diagnosis  of 
w^hich  the  sphygmograph  is  considered  a  valuable  aid,  are  : 
aortic  regurgitation,  aortic  obstruction,  mitral  regurgita- 
tion, and  mitral  obstruction. 

Aortic  regurgitation  consists  of  an  insufficiency  of  the 
aortic  semilunar  valves,    and  consequently  some  of  the 


212      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGl^ 

blood  will  be  forced  back  into  the  left  ventricle  by  the 
force  of  the  elastic  walls  exerted  upon  the  blood  which  is 
forced  into  the  aorta  at  each  ventricular  systole;  the  result 
is  that  the  walls  of  the  arteries  will  relax  much  more 
quickly.  This  is  indicated  in  the  sphygmographic  tracing 
by  the  suddenness  of  the  line  of  descent. 

Aortic  obsfmcfion  is  a  lesion  in  which  during  the  ventri- 
cular systole  the  blood  is  forced  but  gradually  into  the  arte- 
ries. This  is  indicated  by  an  obliquity  of  the  ascending 
line,  w^hich  is  interrupted  and  assumes  a  more  oblique 
course  as  the  summit  is  reached.  This  peculiarity  in  the 
tracing  is  produced  by  the  gradual  distension  of  the  arte- 
rial walls. 

Mitral  regurgitation  is  caused  by  an  insufficiency  of  the 
mitral  valve,  so  that  during  the  ventricular  systole  a 
quantity  of  blood  is  forced  back  into  the  auricle,  thus 
diminishing  the  quantity  of  blood  forced  into  the  arterial 
system,  and  causing  a  consequently  slower  reaction  of  the 
arterial  walls  upon  the  column  of  blood  in  them.  This  is 
indicated,  first,  by  the  shortness  of  the  ascending  line; 
second,  by  the  great  obliquity  of  the  descending  line  in  its 
upper  portion. 

Mitral  obstruction  is  a  lesion  in  which  during  the  auri- 
cular contraction  only  a  small  quantity  of  blood  is  forced 
into  the  left  ventricle  ;  consequently,  during  the  systole  of 
this,  only  a  small  quantity  of  blood  is  forced  into  the  arte- 
rial system  ;  the  blood-pressure  is  therefore  small,  as  rec- 
ognized by  the  easily  compressed  pulse.  It  is  for  this 
reason  that  the  sphygmogram  show^s  no  peculiarity  except 
a  smallness  and  irregularity  of  the  ascent  and  descent  of 
the  line. 

The  exact  clinical  value  of  the  sphygmograph  is  not 
fully  determined,  but  it  is  evident  that  it  is  of  great  use  in 
determining  the  extent  of  certain  valvular  lesions  and  the 
degree  of  pathological  changes  in  the  arterial  walls  by  re- 
peated sphygmographic  observations  upon  a  patient.     The 


THE  BLOOD   CIRCULATION  IN  THE   FCETUS.  213 

clinician  is,  to  a  certain  extent,  enabled  to  also  determine 
the  progress  of  valvular  lesions  and  of  cardiac  and  arterial 
structural  changes. 

The  Blood  Circulation  in  the  Foetus. 

The  foetus  receives  its  blood  from  the  mother  through 
the  placental  vessels,  and  the  venous  blood  is  not  oxygen- 
ized in  the  lungs  of  the  foetus,  because  it  does  not  breathe; 
it   is   therefore   returned   by  the  placental  vessels  to  the 
mother.     The  foetal  heart  presents  certain  peculiarities. 
The  septum  between  the  two  auricles  has  an  opening,  the 
foramen  ovale,  by  w-hich  the  right  auricle  communicates 
directly  with  the  left;  this  opening  has  a  prominent  bor- 
der, the  annulus  ovalis,  which  projects  into  the  right  auri- 
cle.    Between  the  opening  of  the  inferior  vena  cava  and  the 
auriculo-ventricular  opening  there   is   another   projection 
from  the  surface  of  the  auricular  cavity ;  this  is  known  as 
the  Eustachian  valve,  and  is  believed  to  direct  the  current 
of  the  blood  from  the  venae  cavge  toward  the   foramen 
ovale.     The  latter  opening  closes  immediately  after  birth ; 
the  remains  of  it  and  those  of  the  obliterated  Eustachian 
valve  and  annulus  ovalis  remain  visible  even  in  the  heart 
of  the  adult.     The  foetus  receives  arterial  blood  from  the 
mother — i.e.,  from   the  placenta— by  the  umbiliccd  vein, 
which  is  contained  in  the  umbilical  cord.     The  umbilical 
vein  enters  the  abdomen  of  the  foetus  at  the  umbilicus;  in 
the  abdomen  it  passes  along  the  suspensory  ligament  of 
the  liver  to  the  under-surface  of  that  organ,  where  it  gives 
off  branches  to  the  left  lobe  and  to  the  lobus  quadrcdus 
and  lobus  Spigelii  of  the  liver.     The  umbihcal  vein  then 
continues  to  the  transverse  fissure,  and  here  it  divides  into 
two  branches;  one  of  these  joins  the  portal  vein  and  enters 
the  right  lobe;  the  other,  called  the  ductus  venosus,  passes 
upward  and  joins  the  left  hepatic  vein  at  its  junction  with 
the  inferior  vena  cava;  this  vessel  therefore  receives  the 
blood  from  the  portal  vein,  the  hepatic  veins,  the  blood 


214     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

from  those  branches  of  the  umbiKcal  vein  which  are  dis- 
tributed to  the  hver,  the  blood  from  the  ductus  venosus, 
and,  lastly,  the  venous  blood  from  the  lower  part  of  the 
body  of  the  foetus.  The  inferior  vena  cava  conveys  the 
blood  to  the  right  auricle  of  the  foetal  heart,  and  from  this 
it  passes,  guided  by  the  Eustachian  valve,  through  the 
foramen  ovale  into  the  left  auricle;  this  also  receives  a 
small  quantity  of  blood  from  the  foetal  lungs  by  the  pul- 
monary veins.  From  the  left  auricle  the  blood  passes  into 
the  left  ventricle,  and  from  this  into  the  aorta,  by  which  it 
is  largely  distributed  to  the  head  and  upper  extremities;  a 
small  quantity  only  Y)asses  into  the  descending  aorta.  The 
venous  blood  from  the  head  and  the  extremities  is  returned 
by  the  superior  vena  cava  into  the'  right  auricle,  from 
which  it  passes  into  the  right  ventricle,  and  from  this  into 
the  pulmonary  artery;  but  only  a  small  quantity  of  blood 
is  distributed  to  the  lungs,  because  they  are  solid  in  the 
foetus.  The  larger  quantity  of  the  blood  in  the  pulmonary 
artery  is  conveyed  by  a  short  vessel,  called  the  ductus 
arteriosus,  into  the  descending  aorta,  by  which  a  portion 
of  it  is  distributed  to  the  lower  part  of  the  body  of  the 
foetus,  while  the  greater  part  is  returned  by  two  vessels, 
the  nmhiliccd  arteries,  to  the  placenta.  The  latter  vessels 
arise  from  the  internal  iliac  arteries,  pass  ujd  the  sides  of 
the  bladder,  then  continue  onward  to  the  umbilicus,  and 
then  along  the  umbilical  cord  to  the  placenta. 

The  peculiarities  of  the  foetal  circulation  may  be  enume- 
rated as  follows: 

1.  The  foetus  receives  arterial  blood  from,  and  returns 
its  venous  blood  to,  the  placenta. 

2.  The  major  portion  of  the  arterial  blood  supplied  to  the 
foetus  passes  first  through  the  liver  of  the  foetus. 

3.  There  are  two  currents  of  blood  in  the  right  ventricle 
— namely,  the  blood  from  the  inferior  vena  cava  passes 
through  the  foramen  ovale  directly  into  the  left  auricle, 


THE   BLOOD    CIRCULATION  IX   THE   FOETUS.  '2 15 

whereas  the  blood  from  the  superior  vena  cava  passes  into 
the  right  ventricle. 

4.  The  head  and  upper  extremities  of  the  foetus  are  sup- 
plied with  blood  from  the  ascending  aorta,  into  which 
vessel  it  passes  from  the  left  ventricle. 

5.  The  lower  part  of  the  body  receives  blood  from  the 
descending  aorta,  which  vessel  receives  the  greater  part  of 
its  blood  through  the  ductus  arteriosus. 

6.  The  lower  extremities  receive  but  a  small  quantity  of 
blood,  because  most  of  the  blood  in  the  descending  aorta 
is  returned  to  the  placenta  by  the  two  umbilical  arteries, 
which  arise  from  the  internal  iliac  arteries. 

7.  The  lungs  of  the  foetus  receive  but  a  small  quantity  of 
blood,  because  the  lungs  at  that  period  of  life  are  solid,  and 
the  venous  blood  of  the  foetus  is  arterialized  in  the  placenta 
of  the  mother. 

8.  The  peculiarities  of  the  structure  of  the  foetal  heart. 
The  changes  in  the  circulatory  system  at  birth  are  the 

following: 

1.  Immediately  after  birth  the  pulmonary  circulation  is 
established,  the  infant  breathes  as  soon  as  born,  and  more 
blood  is  supplied  to  the  lungs,  as  it  is  now  arterialized  in 
the  lungs  of  the  infant. 

2.  The  foramen  ovale  closes  a  few  days  after  birth;  the 
Eustachian  valve  and  annulus  ovalis  become  obliterated. 

3.  The  ductus  arteriosus  becomes  obliterated  soon  after 
birth. 

,.  4.  The   ductus  venosus   also    becomes    obhterated    and 
finally  forms  the  round  ligament  of  the  liver. 

5.  The  umbilical  vein  contracts  into  a  fibrous  band,  which 
is  seen,  in  the  adult,  passing  up  to  the  liver  in  the  fissure 
for  the  ductus  venosus. 

6.  The  umbilical  arteries  become  partly  obliterated;  the 
portions  passing  up  the  bladder  on  each  side  remain  and 
form  the  cystic  arteries,  the  remainder  forms  fibrous  bands. 


216     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY, 
QUESTIONS   AND   ANSWERS. 

Subject. — The  Blood  Circulation. 
Lectures  XXL-XXIII.  inclusive. 

434-.  Name  the  organs  of  the  blood  circulatory  system, 

435.  Give  the  location  of  the  heart. 

436.  Name  the  cavities  of  the  heart. 

437.  Name  the  septa  separating  the  cavities  of  the  heart- 

438.  Describe  the  pericardium. 

439.  What  is  the  endocardium  ? 

440.  Describe  the  right  auricle. 

441.  Name  the  openings  into  the  right  auricle. 

442.  What  is  the  fossa  ovalis;  the  annulus  ovalis;  the 
Eustachian  valve;  the  coronary  valve;  the  tuberculum 
Coweri;  the  musculi  pectinati  ?    Give  location  of  each. 

443.  Describe  the  right  ventricle. 

444.  Name  the  openings  into  the  right  ventricle. 

445.  What  are  the  columnar  carncce  and  chordae  ten- 
dinese  ?    Give  location  of  each. 

446.  Describe  the  pulmonary  semilunar  valves.  Describe 
the  tricuspid  valve. 

447.  Describe  the  left  auricle  and  name  the  openings  into 
it. 

448.  Describe  the  left  ventricle  and  name  the  openings^ 
into  it. 

449.  Describe  the  mitral  valve. 

450.  Name  the  valves  and  the  openings  which  they  guard, 

451.  What  is  the  annulus  atrio-ventricularis  ? 

452.  Give  the  structure  of  the  cardiac  muscular  fibres. 

453.  Describe  the  arrangement  of  the  muscular  fibres  of 
(a)  the  auricles,  (6)  the  ventricles. 

454.  Give  the  blood-supply  to  the  heart  substance. 

455.  Describe  the  nervous  mechanism  of  the  heart. 

456.  Describe  the  circulation  of  the  blood  through  the 
heart. 

457.  What  do  you  understand  by  the  words  diastole  and 
systole  ? 


QUESTIONS   AND    EXERCISES.  217 

45 S.  Describe  in  regular  order  the  events  which  ta.ke 
place  during  one  cardiac  impulse, 

459.  Give  the  duration  of  one  cardiac  impulse. 

460.  Give  the  number  of  heart  beats  in  one  minute  (a)  in 
the  adult  man,  (6)  in  a  new-born  infant. 

461.  Give  the  comparative  duration  of  each  of  the  va- 
rious phases  of  a  cardiac  impulse. 

462.  Describe  the  changes  which  the  heart  undergoes  in 
form  and  in  position  during  a  cardiac  impulse. 

463.  What  do  you  understand  by  the  apex-beat  ?  How 
is  it  produced,  and  where  is  it  normally  perceptible  ? 

464.  Give  the  relative  location  of  the  following  anatomi- 
cal structures  of  the  heart:  the  aortic  valve,  the  pulmonary 
valve,  the  mitral  valve,  the  tricuspid  valve. 

465.  Describe  the  heart-sounds,  their  character,  quality, 
pitch,  duration,  the  mode  of  their  production,  and  place 
where  best  heard. 

466.  Describe  the  structure  of  the  arteries,  capillaries,  and 
veins. 

467.  How  is  the  circulation  of  the  blood  in  the  system 
maintained? 

468.  What  is  meant  by  blood-pressure  ? 

469.  What  are  the  factors  of  the  circulation  of  the  blood 
in  the  arteries,  capillaries,  and  veins  ? 

4T0,  What  is  the  rapidity  of  the  flow  of  blood  in  the 
aorta,  and  what  is  it  in  the  capillaries  ? 

471.  What  do  you  understand  by  the  tonus  of  the  blood- 
vessels ? 

472.  Describe  the  nervous  mechanism  of  the  blood- 
vessels. 

473.  What  do  you  understand  by  the  pulse  ? 

474.  What  does  the  pulse  indicate  ? 

475.  What  is  the  normal  pulse  rate  in  the  human 
adult  ? 

476.  What  is  a  sphygmograph  ?  Describe  Marey's  in- 
strument. 


218     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

477.  How  is  a  cardiac  pulsation  indicated  in  the  sphygmo- 
graphic  tracing  ? 

478.  Explain  what  a  sphygmograni  indicates. 

479.  Describe  the  sphygmographic  tracing  of  the  nor- 
mal radial  pulse. 

480.  Name  the  more  frequent  lesions  of  the  valves  of  the 
heart. 

481.  Describe  the  sphygmographic  tracing  of  the  radial 
pulse  in  the  case  of  (a)  aortic  regurgitation,  (6)  mitral  re- 
gurgitation, (c)  aortic  obstruction,  {d)  mitral  obstruction, 
(e)  loss  of  elasticity  of  the  arterial  walls. 

482.  What  do  you  understand  by  an  intermittent,  a 
remittent,  a  dicrotic  pulse  ? 

483.  Describe  the  foetal  circulation. 

484.  Point  out  the  peculiarities  of  the  foetal  circulatory 
apparatus. 

485.  Describe  the  changes  which  take  place  in  the  circu- 
latory apparatus  after  birth. 

486.  What  is  the  average  rate  of  the  heart-beat  in  (a)  the 
infant,  (6)  the  adult,  (c)  old  age? 

487.  Describe  the  circulation  of  the  blood. 

488.  What  is  the  physiological  cause  of  blushing  ? 
4S9.  Define  systole,  diastole. 

490.  What  causes  the  first  sound  of  the  heart  ? 

491.  Describe  the  factors  which  cause  the  heart-sounds. 

492.  How  do  the  movements  of  the  chest  in  respiration 
influence  the  circulation  ? 

493.  Give  the  shortest  course  a  drop  of  blood  can  take  in 
passing  from  the  left  to  the  right  ventricle  of  the  heart  in 
normal  circulation. 

494.  What  effect  is  produced  on  the  heart's  action  by 
stimulation  of  the  cardiac  inhibitory  centre  ? 

495.  Describe  the  systole  and  diastole  and  their  causes. 

496.  Describe  the  topography  of  the  normal  heart  in  an 
adult  male. 


LECTURE    XXLV. 

RESPIRATION. 

By  the  word  respiration  is  generally  meant  the  rhythmi- 
'Cal  and  alternate  drawing  in  and  forcing  out  of  the  lungs 
-of  a  quantity  of  air.  Respiration  has  for  its  object  the 
introduction  into  the  body  of  the  oxygen  required  for  the 
process  of  combustion,  and  the  elimination  of  the  carbon 
dioxide  formed  in  the  body.  Respiration  is  effected  by  the 
respiratory  apparatus,  which  consists  essentially  of  a  moist, 
permeable  membrane  which  is  in  contact  with  the  exter- 
nal air  on  one  side  and  with  the  blood  on  the  other. 

The  structure  of  the  respiratory  apparatus  differs  in  the 
several  classes  of  animals,  and  is  adapted  to  the  mode  of 
life  and  the  activity  of  the  individual. 

The  respiratory  apparatus  of  man  consists  of  the  air- 
passages  and  the  lungs  ;  the  skin  must  also  be  considered 
an  important  respiratory  organ,  as  through  it  a  constant 
exchange  of  gases  takes  place. 

The  Air- Passages. 

The  nasal  cavities,  the  larynx,  trachea,  and  the  bronchi 
^re  the  organs  of  the  respiratory  system  through  which 
the  air  passes  which  is  inhaled  or  exhaled. 

The  mouth,  the  nasal  cavities  and  their  turbinated  bones, 
and  the  antrum  of  Highmore  on  each  side,  communicat- 
ing with  the  nasal  fossae,  present  large  vascular  mucous 
surfaces  over  which  the  cold  air  passes  before  it  enters  the 

lungs. 

TJie  Larynx. 

The  larynx  is  that  portion  of  the  respiratory  apparatus 


220       LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

which  is  situated  in  the  neck  in  front  of  the  pharynx  and 
above  the  trachea  ;  it  is  composed  of  nine  cartilages,  which 
are  so  held  together  by  ligaments  as  to  form  a  firm  box  for 
the  purpose  of  protecting  its  interior  structures  which  con- 
stitute the  organ  of  voice.  A  number  of  muscles  are  at- 
tached to  the  larynx,  which  effect  the  movements  of  the 
organ  and  its  various  parts  as  required  for  the  production 
of  voice. 

The  larynx  is  supplied  with  nerves  and  blood-vessels. 
Its  interior  forms  a  triangular  cavity,  broad  and  wide 
above,  round  and  narrow  below,  lined  with  mucous  mem- 
brane. It  contains  the  vocal  cords,  and  communicates 
with  the  mouth  and  pharynx  above  and  with  the  trachea 
below.  I  will  give  a  fuller  description  of  the  larynx 
when  speaking  of  it  as  the  organ  of  voice. 

TJie  Trachea. 

The  trachea  is  that  portion  of  the  air- passages  which  is 
commonly  called  the  wind-pipe.  It  is  about  ^  inches  long, 
and  extends  from  the  lower  end  of  the  larynx,  through  the 
neck,  into  the  thoracic  cavity  between  the  pleurae  and  in 
front  of  the  a3Sophagus  to  a  point  opposite  the  fourth  or 
fifth  dorsal  vertebra,  where  it  bifurcates  into  the  two  bron- 
chi, one  for  each  lung. 

The  trachea  is  tubular.  It  is  composed  of  a  number  of 
cartilaginous  rings  which  are  imperfect  behind  and  which 
are  connected  with  each  other  by  a  fibrous  membrane; 
outside  of  this  is  a  layer  of  transverse  and  longitudinal 
muscular  fibres  of  the  non-striated  variety.  The  interior 
of  the  trachea  is  lined  with  mucous  membrane,  which  is 
covered  with  a  single  layer  of  columnar  ciliated  epithelium; 
between  these  are  the  openings  of  numerous  so-called  tra- 
cheal glands,  the  secretion  of  which  serves  to  moisten  the 
mucous  surface;  beneath  the  latter  is  a  thin  layer  of  elastic 
fibres. 

The  cartilaginous  rings  serve  to  maintain  the  lumen  of 


THE   BEONCHI — THE   LUNGS.  221 

the  tube;   they  are   cyhnclrical  and  from  three-fourths  to 
one  inch  in  diameter. 

The  Broyiclii. 

The  trachea  bifurcates  in  the  thoracic  cavity,  opposite 
the  fifth  dorsal  vertebra,  into  the  right  and  left  bronchi. 
The  i^ight  bronchus  is  about  1  inch  long  and  enters  the 
right  lung  opposite  the  fifth  dorsal  vertebra.  The  left 
bronchus  is  about  two  inches  long  and  enters  the  left  lung 
at  a  poiut  opposite  the  sixth  dorsal  vertebra. 

In  the  lung  substance  the  bronchi  ramify  freely,  con- 
stantly diminishing  in  size,  until  in  the  lobules  of  the  lungs 
they  attain  a  size  of  0.4  to  0..5  millimetre — i.e.^  one-fiftieth 
to  one-thirtieth  of  an  inch — in  diameter,  and  finally  open 
into  the  pouch -like  expansions  known  as  the  infundihida. 
The  smaller  bronchi  are  called  hroncliioli. 

The  structure  of  the  bronchi  varies  with  their  size.  The 
larger  bronchi  have  the  same  structure  as  the  trachea;  the 
smaller  bronchi  do  not  contain  cartilaginous  rings,  but 
merely  cartilaginous  laminge  scattered  through  their  walls, 
principally  at  the  points  of  bifurcation.  The  smallest 
bronchi  do  not  contain  any  cartilaginous  masses  in  their 
walls,  but,  instead  of  these,  circular  muscular  fibres.  The 
bronchi  all  contain  a  fibrous  coat  and  muscular  and  elastic 
fibres;  their  interior  is  lined  with  mucous  membrane  cov- 
ered with  ciliated  epithelium.  The  mucous  membrane  of 
the  bronchi  is  moistened  by  the  tenacious  secretion  of 
numerous  goblet-cells  which  are  situated  between  the  epi- 
thelial cells;  this  tenacious  secretion  also  serves  to  retain 
particles  of  dust  which  are  inhaled  with  the  air. 

The  Lungs. 

The  principal  organs  of  the  respiratory  apparatus — 
namely,  the  two  lungs — lie  in  the  lateral  portions  of  the 
thoracic  cavity. 

Each  lung  is  surrounded  by  a  closed  sac  of  serous  mem- 
l)rane,  called  iYiQ  pleura.     This  consists  of  aj^anefaZand  a 


5i22      LECTURES   OX   HUMAX   PHYSIOLOGY   AND    HISTOLOGY^ 

visceral  layer,  and  serves  to  prevent  friction  between  the- 
lung  and  its  parietes.  Tiie  pleurae  are  attached  to  the 
structures  which  comprise  the  root  of  the  lungs.  Each 
lung  is  conical  in  shape,  with  its  base  directed  downward. 
The  cipex  is  pointed  and  extends  about  1  inch  above  the 
first  rib.  The  hase  is  concave  and  rests  upon  the  dia- 
phragm. The  exterior  surface  of  the  lungs  is  convex  and 
is  directed  toward  the  inner  surface  of  the  chest- walls 
anteriorly,  laterally,  and  posteriorly.  The  inner  surface  is 
concave  and  is  directed  toward  the  middle  line.  The  space 
between  the  two  lungs  is  termed  the  mediastinum. 

Each  lung  is  divided  by  a  transverse  fissure  into  an 
upper  and  a  lower  lobe.  The  upper  lobe  of  the  right  lung 
is  generally  divided  by  a  second  fissure,  so  that  this  lung 
consists  of  three  lobes.  Various  structures — namely,  the 
pulmonary  artery  and  veins,  the  bronchial  artery  and 
veins,  nerves,  lymphatics,  and  one  bronchus — enter  and 
leave  the  lung  at  its  inner  surface  a  little  above  the 
centre.  These  structures  are  surrounded  by  areolar  tissue 
and  constitute  the  root  of  the  lung. 

The  lungs  receive  blood  through  two  vessels.  The  hron- 
cliial  artery  conveys  to  the  lung  the  blood  intended  for  its 
nutrition.  The  vessel  enters  the  lung  at  its  root,  and  in  its 
course  through  the  lung  follows  the  ramifications  of  the 
bronchi  and  bronchioles,  distributing  numerous  branches 
to  the  walls  of  these  and  to  the  difi'erent  structures  com- 
posing the  lungs.  The  bronchial  veins  return  the  venous 
blood  from  the  lungs  and  leave  them  at  the  roots.  The 
jmhnonary  artery  carries  venous  blood  from  the  heart  to 
the  lungs.  The  artery  enters  the  lung  at  its  root ;  in  its 
course  it  follows  the  ramifications  of  the  bronchial  tubes, 
and  finally  divides  into  a  capillary  plexus  which  is  distri- 
buted to  the  walls  of  the  air-cells  ;  here  the  blood  takes 
up  oxygen  from  the  air,  and  is  returned  by  the  pulmonary 
veins  as  arterial  blood  to  the  heart. 

The  lymph-vessels  of  the  lungs  begin  as  minute  channels 


THE   STRUCTUKE   OF   LUNG-TISSUE.  223r 

in  the  walls  of  the  air-cells.     The  vessels  follow  the  course- 
of  the  bronchi  and  leave  at  the  root  of  the  lung. 

The  nerves  supplying  the  lung-structures  are  derived 
from  the  pulmonary  plexus,  which  is  formed  by  fibres 
from  the  sympathetic  and  pneumogastric  nerves. 

The  weight  of  both  lungs  is  about  42  ounces,  or  1, 340 
grammes.  The  right  lung  is  about  two  ounces  heavier 
than  the  left. 

To  the  touch  the  lungs  feel  spongy,  and  crepitate  when 
handled,  owing  to  the  pressure  of  air  in  them.  Lung- 
tissue  has  a  specific  gravity  of  0.345  to  0.745,  and  conse- 
quently floats  on  water. 

The  color  of  the  lungs  is  pinkish-white  in  childhood,  but 
becomes  slate-colored  and  spotted  in  adult  life;  this  dis- 
coloration, which  advances  with  age,  is  due  to  the  deposi- 
tion of  particles  of  carbonaceous  matter. 

The  relative  extent  of  the  lungs  in  the  thoracic  cavity 
can  be  determined  by  percussion  and  by  auscultation — 
methods  in  which  you  will  receive  practical  instruction. 

Tlie  Structure  of  Lung -Tissue. 

Each  lung  is  externally  covered  by  a  serous  membrane, 
the  visceral  layer  of  the  pleura;  beneath  this  is  a  fibrous- 
coat  which  contains  elastic  fibres,  and  which  sends  pro- 
longations into  the  substance  of  the  lung,  dividing  it  into 
numerous  small  masses  called  lobules. 

The  lobules  of  the  lungs  are  small,  polyhedral  masses  of 
lung-tissue;  they  are  connected  by  interlobular  areolar 
tissue.  A  lobule  consists  of  a  terminal  bronchus,  which 
expands  into  a  pouch  called  the  infundihidnm;  this  has 
numerous  sacculated  recesses,  w^hich  are  called  the  air- 
vesicles,  alveoli,  or  air-cells. 

The  walls  of  the  infundibula  and  their  alveoli  are  com- 
posed of  fibrous  tissue  containing  elastic  and  non- striated 
muscular  fibres,  and  support  the  capillary  plexus  of  the 
pulmonary  artery.     The  interior  of  the  infundibula  is  lined 


234      LECTURES   OX   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

with  the  same  epithehal  cells  which  cover  the  liuiug  of  the 
i^erminal  bronchioles;  the  alveoli,  air- vesicles,  or  air-cells 
are  lined  with  a  layer  of  flat,  man3--siclecl  epithelial  cells. 
The  exchange  between  the  gases  of  the  blood  in  the  capil- 
laries and  those  of  the  inhaled  air  takes  place  through  the 
walls  of  the  alveoli. 

The  total  number  of  such  air-cells  or  alveoli  in  the 
human  lungs  has  been  estimated  to  be  809,500,000,  and 
their  total  respiratory  surface  to  be  81  square  metres. 

The  Mechanism  of  Respiration. 

The  respiratory  act  consists  of  an  inspiration  and  an  ex- 
piration of  air. 

Inspiration  is  the  aspiration  of  air  into  the  air-passages 
and  lungs;  it  is  effected  by  an  expansion  of  the  thoracic 
cavity  in  its  several  diameters;  and  the  lungs,  which,  \vith 
their  outer  surfaces,  are  in  close  contact  with  the  internal 
surface  of  the  chest- wall,  will  follow  any  expansion  of  the 
chest,  owing  to  their  elasticity.  The  expansion  of  the 
lungs  causes  a  decrease  in  the  density  of  the  air  contained 
in  them,  and  consequently  air  will  rush  into  the  lungs 
through  the  air  passages  until  the  density  of  the  air  in  the 
lungs  has  become  equal  to  the  density  of  the  external  air. 

The  expansion  of  the  chest  is  a  muscular  act;  the  verti- 
cal diameter  of  the  thoracic  cavity  is  increased  by  the 
descent  of  the  diaphragm;  the  horizontal — viz.,  the  antero- 
posterior and  lateral — diameters  are  increased  by  the  rais- 
ing of  the  ribs  and  sternum.  The  ordinary  position  of  the 
ribs  is  obliquely  downward  and  forward  from  their  spinal 
to  their  sternal  articulation;  during  inspiration  the  ribs 
are  raised  and  with  them  the  sternum. 

The  muscles  used  during  an  ordinary  inspiration  are: 
the  external  intercostal  muscles,  the  scaleni,  the  levatores 
costarum,  the  serratus  posticus  superior,  and  the  dia- 
phragm. 

During  a  forced   inspiration  the  following  muscles  are 


THE    MECHANISM    OF    RESPIRATION.  ^^5 

used:  the  pectoralis  major  and  minor,  the  serratus  magnus 
anticus,  the  trapezius,  and  the  muscles  of  the  neck. 

Expiration  is  the  act  by  ^'hich  air  is  forced  out  of  the 
lungs  through  the  air-passages  ;  it  is  effected  by  the  re- 
traction of  the  chest- walls  and  consequent  retraction  of  the 
lungs.  During  inspiration  the  ligaments  and  soft  parts  of 
the  chest-walls  are  stretched,  and  the  force  which  they 
exert  when  they  return  to  their  normal  state,  together 
with  the  weight  of  the  chest- walls  and  the  cessation  of 
the  contraction  of  the  muscles  used  during  inspiration,  is 
sufficient  to  effect  an  ordinary  expiration,  daring  which 
the  diameters  of  the  chest-cavity  are  decreased  by  the  re- 
traction of  the  chest- walls  and  the  ascent  of  the  diaphragm. 

By  an  effort  of  the  will  the  thorax  may  be  still  more 
retracted  than  it  is  by  an  ordinary  expiration,  and  a  still 
greater  quantity  of  air  can  be  forced  out  of  the  lungs. 

The  muscles  used  in  such  a,  forced  expiration  sue:  the 
interna]  intercostal  muscles,  the  serratus  posticus  inferior, 
the  quadratus  lumborum,  the  latissimus  dorsi,  and  the 
abdominal  muscles. 

The  respiratory  movements  present  characteristic  types 
in  men,  women,  and  children.  It  will  be  observed  that  in 
men  the  lower  part  of  the  chest  is  more  expanded  than  the 
upper;  this  is  termed  the  inferior  costal  type.  In  women 
the  upper  part  is  most  expanded  ;  this  is  called  the  supe- 
rior costcd  type.  In  children  the  respiratory  movements  are 
largely  effected  by  the  motions  of  the  diaphragm,  as  may 
be  seen  by  the  peculiar  up-and  down  motion  of  the  ab- 
domen; this  peculiarity  is  described  as  the  ahdomincd  type. 

The  adult  human  individual  inhales  and  exhales  at  each 
inspiration  and  expiration  about  30  cubic  inches,  or  500 
cubic  centimetres,  of  air  ;  this  quantity  is  called  the  tided 
or  breathing  air.  The  same  individual  is  capable  of  inhal- 
ing by  a  forced  inspiration  100  cubic  inches,  or  1,600  cubic 
centimetres,  of  air,  in  addition  to  the  30  cubic  inches  already 
taken  in  during  the  ordinary  inspiration.     The  100  cubic 

15 


:^-^(3     LECTURES   OX    HUMAN    PHYSIOLOGY    AND    HISTOLOGY. 

inches  of  air  so  taken  in  by  a  forced  inspiration  are  called 
the  compJemenial  air. 

After  an  ordinary  expiration  a  quantity  of  100  cubic 
inches  of  air  can  be  forced  out  of  the  lungs  by  a  forced  ex- 
piration ;  this  is  called  the  reserve  air. 

After  the  most  forcible  expiration  there  remain  in  the 
lungs  100  cubic  inches  of  air,  which  is  known  as  the 
residual  air. 

The  total  air-capacity  of  the  lungs  is  therefore  330  cubic 
inches,  or  5,200  cubic  centimetres— namely,  100  cubic 
inches  of  residual  air,  100  cubic  centimetres  of  reserve  air, 
30  cubic  centimetres  of  tidal  air,  and  100  cubic  centimetres 
of  complemental  air. 

The  breathing  capacity  is  the  quantity  of  air  which  can 
be  exhaled  after  the  lungs  have  been  filled  by  a  forced  in- 
spiration. This  amount  is  230  cubic  inches — namely,  30 
cubic  centimetres  of  tidal  air,  100  cubic  centimetres  of 
complemental  air  which  was  taken  in  by  the  forced  in- 
spiration, and  100  cubic  centimetres  of  reserve  air  which, 
in  addition  to  the  tidal  and  complemental  air,  can  be  ex 
pelled  from  the  lungs  by  a  forced  expiration. 

The  quantity  of  air  which  is  exhaled  or  inhaled  by  an 
individual  is  measured  by  an  instrument  called  the  spiro- 
meter. The  instrument  consists  of  an  air- reservoir  sus- 
pended over  water.  The  reservoir  communicates  by  means 
of  a  tube  with  the  inhaler  into  which  the  individual  breathes. 
The  quantity  of  air  forced  into  the  reservoir,  or  the  quan- 
tity taken  out  of  the  same,  by  the  inspiration  and  expira- 
tion, is  indicated  on  a  scale  which  communicates  with  the 
air-reservoir. 

The  number  of  respirations  in  the  adult  are  14  to  18  a 
minute,  which  is  about  1  respiration  to  4  cardiac  pulsa- 
tions. The  number  of  respirations  is  increased  by  exercise, 
and  generally  in  all  those  conditions  in  which  the  cardiac 
pulsations  are  increased.  In  children  respiration  is  more 
frequent  than   it   is   in  adults.     In  febrile   conditions  the 


THE   MECHANISM   OF   RESPIRATION.  22? 

respirations  are  increased  in  number  proportionally  with 
the  increase  of  the  cardiac  pulsations.  In  many  pulmo- 
nary diseases  the  number  is  often  greatly  increased. 

The  quantity  of  air  required  by  a  healthy  adult  for  respi- 
ration in  twenty-four  hours  is  about  2,150  cuT3ic  feet — that 
is,  at  the  rate  of  from  16  to  18  respirations  per  minute. 
During  that  time  the  individual  consumes  900  grammes  of 
oxygen  and  exhales  74i  grammes  of  CO.,  and  about  500 
grammes  of  water  in  the  form  of  watery  vapor. 


LECTURE    XXV. 

THE   ATMOSPHERIC   AIR   AND   THE   CHANGES   WHICH   IT 
UNDERGOES  DURING   RESPIRATION. 

The  atmospheric  air  which  we  breathe  is  a  mixture  of 
gases  containing  20.92  percent  of  oxygen,  79.03  per  cent 
of  nitrogen,  and  0.03  to  0.05  per  cent  of  carbon  dioxide. 
Besides  these  the  atmospheric  air  contains  at  all  times  a 
greater  or  less  quantity  of  watery  vapor.  This  quantity 
differs;  it  is  influenced  by  the  location,  temperature,  sea- 
son, geographical  conditions,  and  the  time  of  day. 

The  quantity  of  watery  vapor  in  the  atmosphere  is  mea- 
sured by  means  of  the  hygrometer.  It  will  be  found  to  be 
greater  in  valleys  than  on  mountains;  is  greater  in  winter 
than  in  summer;  greater  when  south  and  west  winds  pre- 
vail than  when  east  and  north  winds  blow;  and  it  is  greater 
in  the  morning  until  sunrise,  and  least  at  noon,  increasing 
again  toward  evening  and  during  the  night. 

Atmospheric  air  often  contains  impurities,  such  as  traces 
of  ammonia,  sulphuretted  hydrogen,  dust,  etc.  Besides 
these  more  common  impurities  the  atmospheric  air  some- 
times contains  substances  which  are  injurious  to  the  health 
of  the  individual  breathing  the  air.  Among  these  impuri- 
ties we  may  mention  the  poisonous  and  irrespirable  gases, 
pathogenetic  substances,  etc. 

The  temperature  of  the  atmospheric  air  is  generally 
lower  than  that  of  the  air  in  the  lungs. 

During  respiration  the  air  undergoes  certain  changes, 
which  may  be  enumerated  as  follows  : 

1.  The  quantity  of  oxygen  is  diminished. 

2,  The  quantity  of  carbon  dioxide  is  increased. 


THE   RESPIRATORY   CHANGES   OF   THE   ATMOSPHERE.      229 

3.  The  volume  is  diminished. 

4.  The  watery  vapor  is  increased. 

5.  The  temperature  is  increased. 

6.  A  small  quantity  of  ammonia  and  organic  matter  is 
added. 

Respiration  consists  of  three  distinct  phases  : 

1.  The  inspiration  and  exhalation  of  the  air. 

2.  The  exchange  of  a  quantity  of  CO^  in  the  blood  of  the 
capillary  plexus  distributed  to  the  walls  of  the  air-cells  of 
the  lungs,  for  a  quantity  of  oxygen  from  the  air  contained 
in  the  alveoli  or  air-cells.  This  exchange  of  gases  is  termed 
the  external  respiration,  and  it  takes  place  through  the 
walls  of  the  capillaries  and  of  the  air-cells. 

3.  The  exchange  of  the  C0„  formed  in  the  tissues  as  a 
product  of  combustion,  for  a  quantity  of  oxygen  from  the 
blood  contained  in  the  capillaries  distributed  to  the  tissues. 
This  exchange  of  gases  is  termed  the  internal  respiration; 
it  takes  place  through  the  walls  of  the  capillaries.  This 
exchange  of  gases  is  due  to  the  physical  processes  known 
as  the  diffusion  and  dissociation  of  gases. 

The  diffusion  of  gases  is  a  phenomenon  which  is  observed 
to  take  place  between  the  particles  of  gases  which  do  not 
combine  chemically.  When  such  gases  come  together  their 
particles  will  tend  to  mix  until  an  equal  mixture  is  ob- 
tained. This  diffusion  takes  place  independently  of  the 
specific  weights  of  the  gases,  and  it  also  takes  place  through 
the  pores  of  an  animal  membrane. 

The  dissociation  of  gases  is  a  phenomenon  where  certain 
gases  will,  under  a  certain  pressure,  unite  chemically  with 
other  substances,  and  where  the  chemical  union  so  pro- 
duced will  dissolve  again  when  the  pressure  required  for 
its  formation  is  decreased  to  a  certain  extent.  This  phe- 
nomenon, according  to  Bonders,  plays  an  important  role  in 
the  respiratory  exchange  of  the  gases. 

If  the  air  in  the  various  portions  of  the  respiratory  ap- 
paratus is  examined,  it  will  be  found  that  the  air  in  the 


230     LECTURES   OX   HUMAN   PHYSIOLOGY   AND    HISTOLOGY, 

alveoli  of  the  lungs  contains  a  greater  percentage  of  CO,  and 
a  smaller  percentage  of  oxygen  than  the  air  in  the  smaller 
bronchi,  and  that  the  air  in  these  contains  also  a  smaller 
percentage  of  oxygen  and  a  larger  percentage  of  CO., 
than  the  air  in  the  larger  bronchi,  and  it  will  also  be  found 
that  the  air  in  the  upper  air-passages  becomes  more  and 
more  similar  to  the  ordinary  atmosphere,  as  regards  its  per- 
centage of  C0„  and  oxygen;  so  that  it  may  be  said  that  the 
air  in  the  various  portions  of  the  respiratory  tract  consists, 
as  it  were,  of  layers  in  which  the  percentage  of  CO^  and 
oxygen  differs.  The  result  is  a  continual  diffusion  of  gases 
in  the  air-passages,  the  oxygen  passing  toward  the  lower, 
and  the  CO^  passing  toward  the  upper,  parts  of  the  same, 
with  the  tendency  to  produce  an  equal  mixture  of  the  gases 
in  all  parts  of  the  respiratory  tract. 

The  exchange  of  the  C0„  in  the  blood  of  the  capillaries 
distributed  to  the  walls  of  the  alveoli,  for  a  quantity  of 
oxj'gen  from  the  air  contained  in  the  alveoli,  and  the  ex- 
change of  the  C0„  formed  in  the  tissues  for  a  quantity  of 
the  oxygen  contained  in  the  blood  of  the  capillaries  sup- 
plying the  tissues,  is  caused  principally  by  the  difference 
in  the  tension  of  these  gases. 

Carbon  dioxide  is  produced  continually  in  the  tissues  as 
the  result  of  combustion.  The  tension  or  pressure  of  this 
gas  in  the  tissues  is  greater  than  the  tension  of  this  gas 
contained  in  the  blood  of  the  capillaries  anastomosing  in  the 
tissues;  the  result  is  that,  owing  to  this  greater  pressure, 
COo  is  taken  up  by  the  blood  and  forms  chemical  com- 
pounds with  its  ingredients. 

The  blood  which  contains  the  CO.  so  taken  up  is  con- 
veyed to  the  lungs,  and  here  the  CO^  is  liberated  from  its 
compounds,  because  the  tension  of  this  gas  in  the  air  in  the 
alveoli  of  the  lungs  is  much  less  than  it  is  in  the  com- 
pounds contained  in  the  blood  of  the  capillaries  supplying 
the  walls  of  the  alveoli,  and  the  result  is  that  the  so  libe- 
rated C0„  passes  from  the  blood  toward  the  air  in  the  alveoli, 


THE   RESPIRATORY   CHANGES    OF   THE   ATMOSPHERE.        231 

owing  to  the  law  of  diffusion  of  gases.  Arterial  blood  con- 
tains about  30  per  cent,  venous  blood  from  35  to  50  per 
cent,  of  CO.,  by  volume.  A  small  portion  of  the  CO.,  is 
contained  in  simple  solution  in  the  plasma;  the  greatest 
portion  is  contained  in  chemical  combination  with  the  so- 
dium of  the  plasma  and  with  ingredients  of  the  blood- 
corpuscles. 

Oxygen  is  constantly  required  for  the  process  of  combus- 
tion in  the  tissues  of  the  body;  it  is  taken  up  by  the  blood 
contained  in  the  capillaries  supplying  the  walls  of  the 
alveoli,  from  the  air  contained  in  these,  because  the  tension 
or  pressure  of  the  oxygen  in  the  air  filling  the  alveoli  is 
much  greater  than  the  pressure  of  this  gas  in  the  blood  of 
the  capillaries  of  the  w^alls  of  the  alveoli. 

Again,  the  oxygen  contained  in  the  blood  of  the  capiUa- 
ries  ramifying  in  the  tissues  passes  toward  these,  because 
the  tension  of  this  gas  in  the  tissues  is  much  less  than  it  is 
in  the  blood  of  the  capillaries  anastomosing  in  the  tissues. 

Oxygen  is  contained  in  the  blood  partly  in  a  simple  solu- 
tion in  the  jDlasma,  but  to  a  greater  extent  in  chemical 
combination  with  the  HO  of  the  red  blood-corpuscles. 

The  exchange  of  the  gases  of  the  atmosphere  with  those 
of  the  air  in  the  alveoli  of  the  lungs,  and  of  the  oxygen  of 
the  air  in  the  alveoli  for  CO2  in  the  pulmonary  capillaries, 
and,  lastly,  the  exchange  of  the  oxygen  in  the  capillaries 
of  the  tissues  for  the  CO,  formed  in  these,  is  caused  mainly 
by  the  difference  in  the  tension  of  these  gases  in  the  atmos- 
phere, in  the  air  of  the  alveoli,  in  the  arterial  and  venous 
blood,  and  in  the  tissues. 

Experiments  made  to  ascertain  the  difference  in  the  ten- 
sion of  these  gases  have  given  the  following  approximate 
results : 

The  tension  of  the  oxygen  in  (a)  the  atmospheric  air  is 
equal  to  158  millimetres  Hg;  (6)  in  the  air  of  the  alveoli, 
27.4  millimetres  Hg;  (c)  in  the  venous  blood,  22  millimetres 
Hg;   id)  in  the  arterial  blood,   29.6  millimetres  Hg:  it  is 


232     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

lowest  in  the  tissues.  The  tension  of  the  CO.,  in  (a)  the 
atmospheric  air  is  equal  to  0.038  millimetre  Hg;  (6)  in  the 
air  of  the  alveoli  of  the  lungs,  27  millimetres  Hg;  (c)  in  the 
venous  blood,  41  millimetres  Hg;  (d)  in  arterial  blood,  21 
millimetres  Hg;  it  is  highest  in  the  tissues. 

Expired  air  shows  a  decrease  of  oxygen.  Inspired  air 
normally  contains  20.92  per  cent  of  oxygen  by  volume; 
expired  air,  16.14  per  cent.  The  balance  is  taken  up  by 
the  blood;  it  is  equal  to  4.78  per  cent  of  the  volume  of  the 
inspired  air.  The  total  weight  of  the  quantity  of  oxygen 
consumed  by  the  healthy  adult  man  in  twenty  four  hours 
is  estimated  to  be  900  grammes. 

Expired  air  shows  an  increase  of  CO^,  due  to  the  elimina- 
tion of  C0„  from  the  blood  in  the  pulmonary  capillaries. 
The  total  weight  of  the  C0„  eliminated  from  the  body  by 
the  healthy  adult  man  in  twenty-four  hours  is  estimated 
to  be  744  grammes. 

This  exchange  of  these  two  gases  is  in  a  certain  propor- 
tion, so  that  for  every  volume  of  oxygen  w^hich  is  taken 
up  into  the  blood  a  little  less  than  an  equal  volume  of  CO^^ 
is  given  off  from  the  blood.  Atmospheric  air  contains  0.03 
to  0.05  per  cent  of  carbon  dioxide;  expired  air  contains 
about  4. 38  per  cent  of  this  gas  in  volume. 

This  shows  that  the  volume  of  C0„  which  is  replaced  for 
the  oxygen  in  the  air  during  respiration  is  about  one- 
fortieth  smaller  than  the  volume  of  oxygen  given  off. 

The  result  is  a  corresponding  decrease  in  the  volume  of 
air  during  the  respiration.  This  decrease  in  the  volume  of 
the  expired  air,  as  compared  with  that  of  the  ins])ired  air, 
is  only  perceptible  when  the  temperature  and  the  percen- 
tage of  moisture  in  the  expired  air  are  the  same  as  those 
of  the  inspired  air.  The  volume  of  the  expired  air  is  really 
greater  than  that  of  the  inspired  air,  but  this  is  due  to  the 
increase  of  the  temperature  and  watery  vapor  in  the  ex- 
pired air. 

The  watery  vapor  of  the  air  is  generally  increased  during 


THE    RESPIRATOKY   CHANGES   OF   THE   ATMOSPHERE.      335 

respiration.  The  degree  of  increase  depends,  first,  upon 
the  quantity  of  watery  vapor  contained  in  the  atmosphere; 
second,  upon  the  temperature  of  the  expired  air;  and, 
third,  upon  the  length  of  time  the  inspired  air  is  retained 
in  the  lungs.  The  watery  vapor  which  is  exhaled  is  pro- 
duced by  the  evaporation  of  the  water  secreted  from  the 
blood  by  the  pulmonary  mucous  membrane.  The  quantity 
of  watery  vapor  exhaled  is  generally  the  quantity  which  i& 
required  to  saturate  the  expired  air.  If,  therefore,  the  in- 
spired air  already  contains  a  large  percentage,  then  but 
little  more  is  required  to  saturate  it,  and  vice  versa.  If 
the  inspired  air  is  retained  in  the  lungs  for  a  longer  time 
its  temperature  is  raised  ;  the  result  is  a  corresponding 
effective  evaporation  of  moisture  from  the  pulmonary 
mucous  membrane,  and  a  resulting  increase  of  watery 
vapor  in  the  expired  air.  It  has  been  estimated  that  the 
quantity  of  water  thus  eliminated  from  the  body  in  twen- 
ty-four hours  is  about  500  grammes. 

The  temperature  of  the  air  is  generally  increased  during 
respiration  to  such  an  extent  that  expired  air  assumes  the 
temperature  of  the  blood — viz.,  98°  to  99°  F.  It  has  been 
observed  that  when  the  temperature  of  the  inspired  air  is 
higher  than  that  of  the  blood  there  is  a  decrease  in  the 
temperature  during  respiration. 

An  examination  of  the  expired  air,  as  compared  with  the 
inspired  air,  shows  an  increase  of  organic  matter  and  of 
free  ammonia.  It  is  estimated  that  the  quantity  of  am- 
monia exhaled  with  the  air  is  about  0.02  gramme  in. 
twenty -four  hours. 


LEOTUEE  XXTL 

THE   NERVOUS   MECHANISM   OF   RESPIRATION. 

The  act  of  respiration  is  induced  and  regulated  by  the 
activity  of  a  centre  which  is  known  as  the  centre  of  respi- 
ration; this  is  located  in  the  floor  of  tlie  fourth  ventricle  of 
the  brain.  It  is  an  automatic  centre;  its  activity  is  ordi- 
narily not  induced  by  stimuli  received  through  peripheral 
nerves. 

The  centripetal  nerves — that  is,  the  nerves  by  which  the 
impulse  for  the  respiratory  movements  is  conducted  from 
the  centre  to  the  periphery — are  the  motor  nerves  of  the 
muscles  coucerned  in  the  respiratory  movements. 

Respiration  is  to  a  limited  extent  under  the  control  of 
the  will.  The  centre  of  respiration  is  also  irritated  by 
stimuli  received  through  peripheral  nerves,  such  as  the 
sensory  nerves  of  the  air-passages  and  lungs;  the  respira- 
tory movements  so  produced  are  essentially  a  reflex  act. 

Ordinarily  the  normal  automatic  activity  of  the  centre 
of  respiration  depends  upon  the  normal  quantity  of  oxygen 
in  the  blood  of  the  brain. 

The  normal  condition  of  respiration  is  described  as  eup- 
noea;  in  this  condition  the  respirations  are  free,  easy,  and 
regular. 

When  the  quantity  of  oxygen  in  the  blood  of  the  brain 
is  abnormally  increased,  then  the  centre  of  respiration  is 
influenced  in  such  a  manner  that  the  respiratory  motions 
become  slower;  they  become  difficult  and  the  expiration  is 
forcible;  this  condition  is  known  as  apnoea. 

When  the  quantity  of  the  oxygen  in  the  blood  of  the 
brain  is  abnormally  decreased,  then  the  centre  of  respira- 


THE    NERVOUS    MECHANISM    OF   RESPIRATION.  :235 

i;ion  is  influenced  in  sucii  a  manner  that  the  respiratory 
motions  become  hurried,  labored,  and  difficult,  and  inspira- 
tion is  more  forcible;  this  condition  is  called  dyspnoea. 
Such  difficult  breathing  is  observed,  for  instance,  at  high 
temperatures;  this  is  due  to  the  greater  and  more  rapid 
consumption  of  oxygen  in  the  tissues  and  its  consequent 
decrease  in  the  blood.  Prolonged  dyspnoea  is  generally  ac- 
companied by  cyanosis,  i.e.,  a  bluish  discoloration  of  the 
skin  and  mucous  membranes;  this  is  due  to  the  decrease  of 
oxygen  in  the  blood.  When,  by  an  obstruction  of  the  air- 
passages,  the  air  is  hindered  from  entering  the  lungs,  or 
when  a  gas  containing  no  free  oxygen  is  inhaled  instead  of 
air,  then  a  condition  is  produced  which  is  known  as  suffoca- 
tion ;  during  this  the  respiratory  movements  are  labored, 
then  there  is  a  spasmodic  contraction  of  the  muscles  of 
respiration,  and  finally  the  respiratory  movements  cease 
entirely,  the  skin  and  mucous  membranes  become  dark, 
almost  black,  and  death  occurs  by  asphyxia,  which  is  a 
want  of  oxygen. 

When  the  quantity  of  carbon  dioxide  in  the  blood  is  ab- 
normally increased  there  will  also  be  dyspnoea,  but  in  this 
condition  the  expirations  are  more  forcible,  whereas  in  the 
dyspnoea  produced  by  a  decrease  of  oxygen  in  the  blood 
the  inspirations  are  more  forcible. 

The  pneumogastric  nerves  contain  fibres  which  are  dis- 
tributed to  the  lungs.  When  the  pneumogastric  nerves  are 
cut  in  the  neck,  then  the  respiratory  motions  become 
slower,  deeper,  and  less  regular.  When  the  central  stump 
•of  the  pneumogastric  is  stimulated  by  an  interrupted  cur- 
rent, the  respiratory  motions  will  become  quicker  and  more 
regular,  and,  by  a  proper  application  of  the  current,  the 
normal  rhythm  and  character  of  the  respiratory  move- 
ments can  be  produced.  These  experiments  tend  to  de- 
monstrate that  the  normal  activity  of  the  centre  of  respira- 
tion is  to  a  certain  extent  regulated  by  stimuli  which,  from 
the  lungs,  are  conducted  to  the  centre  by  the  pulmonary 


23G     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

fibres  of  the  pneumogastric  nerve.  The  irritation  of  certain 
peripheral  sensory  nerves  influences  the  respiratory  move- 
ments. Certain  special  respiratory  acts,  such  as  coughing, 
sneezing,  sighing,  and  yawning,  are  reflex,  being  caused 
by  the  irritation  of  certain  sensory  nerves.  Coughing,  for 
instance,  is  produced  by  an  irritation  of  the  sensory  nerve 
of  the  larynx — namely,  the  superior  laryngeal  nerve,  by 
which  the  stimulus  is  conducted  to  the  centre  ;  the  result 
is  a  closure  of  the  glottis  and  a  sudden,  forcible  expiration 
accompanied  by  the  peculiar  sound  heard  wiien  coughing. 

Irritation  of  the  sensory  nerves  of  the  skin  of  the  head, 
neck,  and  chest — for  instance,  the  application  of  cold  water 
— produces  deep  and  forcible  respiratory  movements  as  the 
result  of  the  stimulation  of  the  centre  of  respiration  by 
stimuli  received  through  peripheral  sensory  nerves. 

From  this  description  of  the  function  of  respiration  you 
will  learn  that  the  sole  purpose  of  this  function  is  to  main- 
tain the  proper  exchange  of  the  gases  of  the  blood — namely, 
of  the  carbon  dioxide  which  is  constantly  formed  in  the 
body  as  the  result  of  the  combustion  of  substances,  for  the 
quantity  of  oxygen  from  the  inspired  air  which  is  required 
for  this  process  of  combustion.  Respiration,  like  the  whole 
physiological  activity  of  the  organism,  depends  upon  the 
proper  exchange  of  these  gases;  this  is  best  shown  by  the 
serious  functional  disturbances  caused  by  any  interference 
with  this  normal  exchange  of  gas. 

To  maintain  a  normal  activity  of  the  respiratory  func- 
tion and  a  proper  exchange  of  the  gases  in  the  blood,  it  is 
not  only  essential  that  the  respiratory  apparatus  be  in  a 
normal  condition,  but  also  that  the  atmosphere  we  breathe 
be  normal  in  quantity,  quality,  and  condition. 

It  is  essential  (1)  that  we  breathe  air  or  a  mixture  of 
gases  which  contains  oxygen  in  proper  quantity  and  in  a 
form  which  does  not  prevent  its  being  taken  up  by  the 
blood. 

(2)  That  the   mixture  of  gases  we  breathe   should  not 


THE   NERVOUS    MECHANISM    OF    RESPIRATION.  237 

interfere  with  the  ehmination  of  carbon  dioxide  from  the 
blood. 

(3)  That  the  pressure  which  the  atmosphere  exerts  upon 
the  surfaces  of  the  body  be  within  certain  hmits. 

To  understand  this  more  fuhy  I  will  describe  to  you  the 
effects  produced  when  these  conditions  are  changed. 

Oxygen  is  the  essential  ingredient  of  air.  If  the  mixture 
of  gases  we  breathe  contains  no  oxygen,  death  from  suffo- 
cation quickly  takes  place,  even  if  the  mixture  of  the  gases 
breathed  does  not  interfere  with  the  elimination  of  CO^. 
Normal  atmospheric  air  contains  20.92  per  cent  of  oxygen 
by  volume;  expired  air  still  contains  16.1-1  per  cent  of  this 
gas;  if  this  percentage  is  even  decreased  to  9  per  cent  no 
special  influence  on  respiration  is  produced;  when  de- 
creased to  S  per  cent  great  inconvenience  is  experienced; 
at  7  percent  dyspnoea  is  caused;  and  when  reduced  to  3 
per  cent  death  results  in  a  short  time  from  want  of  oxygen. 

A  decrease  in  the  quantity  of  oxygen  in  the  atmosphere 
causes  its  decrease  in  the  blood,  owing  to  the  decreased 
tension  of  this  gas  in  the  air  contained  in  the  alveoli  of  the 
lungs.  The  dyspnoea  produced  by  this  condition  is  due  to 
the  influence  on  the  centre  of  respiration.  An  increase  of 
oxygen  in  the  atmosphere  has  no  effect  on  respiration  and 
causes  but  a  small  increase  of  oxygen  in  the  blood. 

Carbon  dioxide  (COJ  is  contained  in  atmospheric  air 
only  in  a  very  small  quantity — viz.,  about  0.03  to  0.05  per 
cent.  The  gas  is  constantly  produced  in  the  body  and  ex- 
haled with  the  expired  air.  Breathing  in  a  closed  room 
brings  about  a  decrease  of  the  oxygen  in  the  air;  CO^  is 
constantly  increased,  and  the  volume  of  the  atmosphere  in 
the  room  is  decreased.  If  the  CO^  in  the  atmosphere  is 
present  to  such  an  extent  that  its  tension  in  the  atmosphere 
is  greater  than  in  the  blood,  then  the  C0„  elimination  from 
the  blood  ceases;  in  fact,  CO^  re-enters  the  blood  and  dysp- 
jioea  and  rapid  death  are  the  result. 

The  dyspnoea  produced  by  such  accumulation  of  CO,  in 


238     LECTURES   ON   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

the  blood  differs  from  that  produced  by  a  diminution  of 
the  oxygen,  in  that  it  is  short  and  not  accompanied  by 
muscular  spasms  and  convulsions,  and  in  that  all  respira- 
tory motions  soon  cease.  Breathing  in  a  small,  closed 
room  uses  up  the  oxygen  before  sufficient  C0„  has  accumu- 
lated in  the  atmosphere  to  prevent  its  elimination  from  the- 
blood;  the  result  is  that  dyspnoea  and  suffocation  are  pro- 
duced by  want  of  oxygen  in  the  blood.  Breathing  in  a 
large,  closed  room  causes  the  accumulation  of  CO2  in  a  suf- 
ficient amount  to  bring  about  dyspnoea  and  death  before 
the  quantity  of  oxygen  is  sufficient  to  interfere  with  the 
respiration. 

The  nitrogen  of  the  air  is  an  indifferent  gas — that  is,  one 
which  has  no  effect  on  respiration  and  does  not  interfere 
with  the  exchange  of  oxygen  and  carbon  dioxide;  it  may 
be  replaced  by  any  other  indifferent  gas,  such  as  hydrogen, 
without  producing  any  marked  effect  on  respiration.  The 
presence  of  irrespirahJe  or  of  poisonous  gases  in  the  aii',  or 
the  breathing  of  such,  seriously  interferes  with  respiration 
and  the  subsequent  exchange  of  the  gases  of  the  blood. 
Irrespirahle  gases  are  those  which  irritate  the  mucous 
membrane  of  the  respiratory  tract  and  so  cause  abnormal 
respiratory  motions;  such  gases  are  bromine,  chlorine,  fluo 
line,  etc. 

Poisonous gdi^es  are  those  which  produce  chemical  changes 
in  the  blood  ingredients  and  so  interfere  with  the  tak- 
ing of  oxygen  or  the  elimination  of  C0„;  such  gases  are 
carbonic  oxide  (CO),  cyanic  acid,  hydrogen  sulphide,  etc. 
They  deoxidize  the  HO  of  the  red  blood-corpuscles,  with 
which  they  unite  chemically,  and  thus  prevent  the  taking 
up  of  oxygen. 

Nitrous  oxide  (N„0),  or  laughing  gas,  is  a  gaseous  com- 
pound which  is  frequently  used  in  dental  practice  to  produce 
general  narcosis;  the  narcosis  is  of  short  duration  and  is  pro- 
duced by  the  effect  of  the  gas  on  the  nervous  system.  Air 
containing  ozone  in  large  quantities  has  a  similar  effect. 


THE   NERVOUS   MECHANISM   OF  RESPIRATION.  239 

Both  of  these  gases  are  known  as  narcotizing  gases;  they 
do  not  interfere  with  respiration. 

The  atmosphere  often  contains  impurities  which  are  in- 
jurious; such  impurities  are  dust,  exhaled  organic  matter, 
micro-organisms  such  as  germs  of  disease — as,  for  instance, 
of  diphtheria,  pneumonia,  influenza,  tuberculosis,  malarial 
diseases,  pertussis,  etc.  Eooms  occupied  by  many  indi- 
viduals, such  as  school-rooms,  factory- rooms,  hospital- 
wards,  etc.,  are  often  filled  with  air  which  is  contaminated 
with  impurities  and  in  which  the  percentage  of  CO^  is  un- 
duly large  ;  to  prevent  such  conditions  it  is  necessary  that 
these  rooms  be  thoroughly  ventilated  to  admit  fresh  air. 

The  air  surrounding  all  bodies  exerts  an  even  pressure 
upon  the  free  surfaces,  owing  to  its  weight ;  this  is  called 
the  atmospheric  pressure ;  it  is  measured  by  the  use  of  the 
instrument  known  as  the  barometer.  This,  in  its  simplest 
form,  consists  essentially  of  a  box  which  communicates 
with  a  glass  tube  ;  this  and  the  box  are  partially  filled 
with  mercury.  The  space  above  the  column  of  mercury  in 
the  glass  tube  is  a  vacuum.  The  pressure  of  the  atmos- 
phere upon  the  surface  of  the  mercury  in  the  box  forces 
the  column  of  mercury  in  the  glass  tube  upward  ;  any 
variations  in  the  atmospheric  pressure  are  indicated  by  a 
rise  or  fall  of  this  mercurial  column.  The  glass  tube  is 
graduated  into  millimetres  or  inches,  and  the  atmospheric 
pressure  is  said  to  be  so  many  millimetres  or  inches  Hg, 
according  to  the  mark  at  which  the  mercurial  column  in 
the  glass  tube  of  the  barometer  stands. 

The  average  atmospheric  pressure  at  the  level  of  the  sea 
and  at  60°  F.  is  760  millimetres  or  30  inches  Hg.  Minor 
variations  are  produced  by  changes  in  the  temperature  and 
in  the  degree  of  humidity  of  the  air  ;  an  increase  of  these 
produces  an  increase  of  the  atmospheric  pressure. 

These  minor  variations  of  the  atmospheric  pressure  have 
no  marked  effect  on  the  respiration,  whereas  greater  vari- 
ations produce  serious  disturbances,  not  only  of  the  respi- 


240     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

ration  and  the  exchange  of  ^^ases,  but  also  of  the  circula 
tion  and  other  vital  functions. 

A  great  increase  of  the  normal  atmospheric  pressure  has 
the  following  effect  : 

The  respirations  become  slower,  easier,  and  less  deep; 
the  skin  is  pale  and  dry;  the  secretions  from  the  skin  and 
mucous  surfaces  are  diminished;  speech  is  difficult  and  the 
voice  is  changed;  the  hearing  is  sharp,  but  there  is  pain 
owing  to  the  pressure  on  the  membrana  tympani.  The 
quantity  of  oxygen  in  the  blood  is  increased,  oxidation  is 
more  active,  and  the  consequent  production  of  C0„  is  in- 
creased; the  elimination  of  C0„  from  the  body  is  not  inter- 
fered with  ;  there  is  congestion  of  the  internal  viscera. 
These  phenomena  are  often  observed  in  people  working 
under  water. 

A  great  decrease  of  the  normal  atmospheric  pressure  has 
the  reverse  effect.  The  skin  and  raucous  surfaces  become 
red  and  swollen,  owing  to  the  decrease  of  the  pressure  upon 
them.  The  secretions  of  the  skin  and  mucous  surfaces  are 
increased  ;  often  there  is  hemorrhage  from  the  mucous  sur- 
faces. The  congestion  of  the  surfaces  of  the  body  produces 
aneemia  of  the  internal  organs.  The  limbs  become  heavier, 
because  the  muscles  alone  must  hold  the  ball  and  socket 
joints  in  place,  while  under  normal  conditions  the  atmos- 
pheric pressure  plays  an  important  role  in  this.  The  res- 
pirations become  quicker  and  more  difficult  ;  inspiration 
especially  is  labored  ;  the  quantity  of  the  oxygen  in  the 
blood  is  decreased ;  the  voice  is  altered,  hearing  dif- 
ficult ;  there  is  pain  owing  to  the  pressing  out  of  the  tym- 
panum. When  the  atmospheric  pressure  is  decreased  to 
240  millimetres  Hg,  death  occurs  under  the  symptoms 
mentioned.  Aeronauts  have  ascended  in  balloons  to  a 
height  of  8,000  metres  and  found  the  atmospheric  pressure 
to  be  280  millimetres  Hg. 

Before  finishing  this  subject  I  will  speak  of  the  respira- 
tory function  of  the  skin. 


QUESTIOXS   AXD   EXERCISES.  241 

It  has  been  demonstrated  by  experiments  that  through 
the  skin  there  takes  place  a  constant  elimination  of  CO, 
and  the  taking  up  of  an  equal  volume  of  oxygen.  How- 
ever, the  respiratory  activity  of  the  skin  is  very  small  as 
compared  with  that  of  the  respiratory  apparatus. 


QUESTIONS   AND   EXERCISES. 

Subject. — The  Respiration. 
Lectures  XXIV. -XXVL  inclusive. 

497.  What  is  meant  by  respiration  ? 

498.  Xame  the  organs  composing  the  respiratory  appa- 
ratus in  man. 

499.  What  are  the  pleurae  ?     Describe  them. 

500.  Give  a  short  description  of  the  larynx. 

501.  Describe  the  trachea. 

502.  Describe  the  structure  of  the  bronchi,  and  point  out 
the  differences  in  the  structure  of  the  larger,  the  smaller, 
and  the  smallest  bronchi. 

503.  Give  a  short  description  of  the  cross  anatomy  of  the 
lungs. 

504.  Xame  the  structures  composing  the  root  of  a  lung. 

505.  Describe  the  structure  of  lung-tissue. 

506.  Describe  the  circulation  of  the  blood  in  the  lungs. 

507.  Why  does  the  normal  lung-tissue  float  on  water  ? 

508.  What  do  3^ou  understand  by  external  and  what  by 
internal  respiration  ? 

509.  Give  the  composition  of  the  atmosphere. 

510.  Xame  the  impurities  in  the  atmosphere. 

511.  AVhat  is  tidal  air  {  complemental  air  ?  reserve  air  ? 
Give  the  Cjuantity  of  each. 

512.  What  is  the  air  capacity  of  the  lungs,  and  what  is 
the  respiratory  capacity  ? 

513.  Give  the  number  of  respirations  per  minute. 

16 


242     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

514.  What  are  the  changes  which  air  undergoes  during 
respiration  ? 

515.  What  do  you  understand  by  the  diffusion  and  what 
by  the  dissociation  of  gases  ? 

51H.  What  is  the  main  factor  in  the  respiratory  exchange 
of  the  gases  oxygen  and  carbon  dioxide  i    Explain. 

517.  What  is  the  tension  of  the  oxygen  in  the  atmos- 
phere ?  in  the  air  of  the  alveoh  ?  in  the  blood  of  the  pul- 
monary capillaries  ?  in  arterial  blood  ?  and  how^  does  its 
tension  in  these  compare  with  its  tension  in  the  tissues  ? 

518.  What  is  the  tension  of  the  carbon  dioxide  in  the 
atmosphere  i  in  the  air  of  the  alveoli  ?  in  venous  blood  ?  in 
arterial  blood?  and  how  does  its  tension  in  these  compare 
with  its  tension  in  the  tissues  ? 

519.  How  are  an  ordinary  inspiration  and  an  ordinary 
expiration  effected,  and  what  muscles  are  usad  in  these 
-acts  ? 

520.  How  are  a  forced  inspiration  and  a  forced  expiration 
effected,  and  what  muscles  are  used  in  these  acts  ? 

521.  Describe  the  nervous  mechanism  of  respiration. 

522.  How  is  the  centre  of  respiration  affected  by  an  in- 
crease of  the  oxygen  in  the  blood,  and  how  by  a  decrease? 

523.  What  is  the  effect  on  the  respiratory  motions  ? 

524.  Define  eupnoea,  dypsnoea,  apnoea,  suffocation,  as- 
phyxia. 

525.  What  is  the  minimum  percentage  of  oxygen  which 
a  volume  of  air  must  contain  in  order  to  support  life? 
What  would  be  the  effect  produced  by  decreasing  this  per- 
centage ? 

526.  At  what  percentage  of  the  CO^  in  a  volume  of  air 
would  COo  poisoning  be  produced  ?  Describe  the  symp- 
toms. 

527.  What  is  the  difference  in  the  symptoms  produced 
by  a  want  of  oxygen  in  the  blood  and  those  produced  by 
an  accumulation  of  CO,  ? 

528.  What  is  meant  by  atmospheric  pressure  ? 


QUESTIONS   AND    EXERCISES.  243 

529.  What  is  the  pressure  of  the  atmosphere  at  the  level 
of  the  sea  and  at  60°  F.  ? 

530.  What  causes  the  common  minor  deviations  of  at- 
mospheric pressure  ? 

531.  What  are  the  effects  produced  by  a  great  increase 
and  those  produced  by  a  great  decrease  of  the  atmospheric 
pressure  ?    Explain. 

532.  Why  is  the  effective  ventilation  of  rooms  essential 
for  the  welfare  of  the  individuals  occupying  them  ? 

533.  What  would  be  the  result  caused  by  breathing  in  a 
small,  closed  room,  and  what  the  result  by  breathing  in  a 
large,  closed  room  ? 

534.  What  is  the  total  quantity  of  oxygen,  by  weight, 
consumed  by  a  healthy  human  adult  in  twenty-four  hours  ? 

535.  What  is  the  total  quantity  of  CO^,  by  weight,  elimi- 
nated by  a  healthy  human  adult  in  twenty-four  hours  ? 

536.  How  do  the  number  of  respirations  compare  with 
the  frequency  of  the  pulse  ? 

537.  Explain  in  short  how  coughing,  sneezing,  yawning, 
and  laughing  are  produced. 

53S.  What  muscles  are  engaged  in  ordinary  inspiration? 
What  muscles  are  involved  in  extraordinary  or  forced  ex- 
piration ? 

539.  What  post-mortem  test  should  be  applied  to  prove 
that  air  had  entered  the  lungs  of  a  supposedly  stillborn 
child? 

540.  Define  the  functions  of  the  mucous  membrane  of 
the  respiratory  tract. 

541.  Where  is  the  respiratory  centre  ? 

542.  How  much  air  is  required  for  normal  respiration 
during  twenty-four  hours  ? 

543.  State  the  changes  in  the  diameter  of  the  chest  in 
inspiration  and  in  expiration. 

544.  Give  the  physiology  and  the  mechanism  of  respira- 
tion. 

545.  Explain  the  process  of  expiration. 


244      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

546.  Where  aod  how  is  the  blood  changed  from  arterial 
to  venous  ?    From  venous  to  arterial  ? 

547.  What  effect  has  respiration  on  the  blood  ? 

548.  Describe  in  full  a  normal  respiration. 

549.  Give  the  causes   of   perverted   function  producing 
dyspnoea  and  asphyxia. 

550.  How  much  oxygen    is    abstracted  by  respiration 
from  every  volume  of  air  inhaled  ? 

551.  What  is  the  object  of  respiration  ? 

552.  Is  respiration  purely  a  voluntary  act  ?    Explain. 


LEOTUEE  XXYir. 

ASSEVIILATION. 

By  the  term  assimilation  is  meant  the  transformation  of 
the  absorbed  nutritive  materials  into  the  chemical  ingredi- 
ents of  the  body.  These  transformations  consist  of  chemi- 
cal, probably  synthetical,  changes;  the  highest  product  of 
these  processes  is  the  living  protoplasm  of  the  cells.  The 
development,  growth,  and  regeneration  of  the  tissues 
of  the  body  are  the  results  of  the  constant  assimilative 
changes  of  the  nutritious  materials  absorbed  in  the  circu- 
lation. 

The  first  substances  formed  as  the  result  of  these  pro- 
cesses are  the  ingredients  of  the  blood  and  lymph,  from 
which,  by  further  assimilative  changes,  the  various  ingre- 
dients of  the  tissues  are  formed. 

The  ingredients  of  the  blood  are  partly  taken  up  as  such 
during  absorption — for  instance,  the  water  and  the  salts. 
The  specific  ingredients  of  the  blood — namely,  the  blood- 
corpuscles — are  formed  in  cei'tain  organs  as  the  product  of 
assimilative  changes  which  certain  materials  of  the  blood 
undergo  in  these  organs. 

The  erythrocytes  are  formed,  in  post-embryonal  life,  in 
the  red  marrow  of  the  bones.  The  latter  consists  of  a 
delicate  network  of  adenoid  tissue,  which  is  freely  perme- 
ated by  a  capillary  network  and  which  contains  lymphoid 
corpuscles;  in  it  are  also  seen  rounded,  nucleated  cells 
which  contain  a  reddish  protoplasm.  After  a  great  loss  of 
blood  numerous  such  cells  are  seen  in  the  blood;  they  are 
called  erythroblasts,  and  it  is  believed  that  they  originate 
from  the  lymphoid  cells  of  the  red  marrow  of  the  bones. 


24:6     LECTURES   ON'   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  ha?inoglobin  in  these  new-formed  erythrocytes  is  the 
product  of  assimilative  changes  in  the  protoplasm  of  the 
lymphoid  cells.  In  the  embryo  the  erythrocytes  originate 
in  a  similar  manner  in  the  liver  from  the  leucocytes  con- 
veyed to  the  liver  with  the  blood  of  the  splenic  vein. 

The  leucocytes  originate  in  the  spleen  and  in  the  lymph- 
atic glands.  The  spleen  is  called  the  vascular  gland,  be- 
cause a  large  amount  of  blood  is  contained  in  its  substance^ 
and  because  its  main  function  is  to  produce  blood-ingre- 
dients—namely, white  blood-corpuscles.  The  spleen  is 
situated  in  the  left  hypochondrium  beneath  the  diaphragm; 
its  exterior  surface  is  oval,  its  inner  portion  concave  and 
is  called  the  hilus,  at  which  vessels  and  nerves  enter  and 
leave  the  organ. 

Tiie  structure  of  the  spleen  is  similar  to  that  of  the 
lymphatic  glands.  It  has  an  external  peritoneal  covering; 
beneath  this  is  a  fibrous  layer  which  contains  elastic  and 
non-striated  muscular  fibres;  this  is  called  the  capsule. 
From  it  prolongations  pass  throughout  the  organ,  which  in 
their  course  surround  the  structures  which  enter  and  leave 
at  the  hilus.  Other  prolongations  from  this  fibrous  capsule 
pass  into  the  substance  of  the  organ;  they  are  called  trabe- 
ciUce,  and  divide  the  organ  into  numei'ous  compartments. 
These  fibrous  structures  constitute  the  sU^oma  of  the  or- 
gan, and  in  its  meshes  are  found  the  structures  which  con- 
stitute the  pulp  of  the  spleen. 

The  spleen-pulp  is  of  a  dark-reddish  color  and  a  brittle 
consistence;  it  is  composed  of  branching  connective-tissue 
cells  which  anastomose  with  their  branches;  the  interstices 
between  these  cells  are  filled  with  blood. 

The  blood-supply  to  the  spleen  is  through  the  splenic 
artery,  a  comparatively  large  vessel,  which,  before  enter- 
ing the  organ  at  the  hilus,  divides  into  several  branches; 
these  pass  along  and  are  supported  by  the  fibrous  trabeculae 
in  the  organ,  until  after  a  short  course  they  divide  into 
bundles  of  straight  arterioles  called  peniciUi,  which  pene- 


ASSIMILATION.  24:7 

trate  the  organ  in  all  directions.  The  Avails  of  these  arteri- 
oles gradually  change;  their  fibrous  coat  thickens  and  is 
transformed  into  adenoid  tissue  consisting  of  a  loose  retic- 
ulum and  presenting  here  and  there  spheroidal,  thickened 
masses  of  adenoid  or  lymphoid  tissue  which  are  called 
Maljnghian  corpuscles;  these  contain  lymphoid  corpuscles. 
The  arterioles  finally  break  into  a  capillary  plexus;  the 
capillaries  ramify  in  the  pulp  of  the  organ;  finally  their 
walls,  being  composed  of  lymphoid  tissue,  become  oblite- 
rated, are  no  longer  tubular,  and  their  lymphoid  cells  be- 
come branched  and  anastomose  with  the  branched  con- 
nective-tissue cells  which  constitute  the  spleen-pulp;  the 
blood  of  the  capillaries  fills  the  interstices  between  these 
cells.  It  is  probable  that  here  the  materials  of  the  blood 
undergo  assimilative  changes  which  result  in  the  produc- 
tion of  leucocytes. 

The  veins  of  the  spleen  arise  from  the  interstices  between 
the  cells  of  the  spleen-pulp;  in  their  course  through  the 
organ  they  frequently  anastomose,  and  finally  they  unite 
to  form  one  vessel,  the  splenic  vein,  which  leaves  at  the 
hilus  of  the  organ  and  opens  into  the  portal  vein.  The 
spleen  is  also  freely  supplied  with  lymphatics  and  nerve- 
fibres  ;  the  latter  are  distributed  to  walls  of  the  blood- 
vessels and  to  the  nou- striated  muscular  fibres  of  the  organ. 

The  fact  that  the  spleen  is  the  principal  organ  for  the 
production  of  leucocytes  is  demonstrated  by  their  enor- 
mous increase  in  number  in  the  blood  of  the  splenic  vein 
as  compared  with  their  number  in  the  blood  of  the  splenic 
artery. 

In  the  artery  the  proportion  is  1  white  to  60  red;  in  the 
vein  it  is  1  white  to  2,200-2,400  red  corpuscles.  The  fact 
that  the  lymphatic  glands  are  also  organs  in  which  leuco- 
cytes are  formed  is  clearly  shown  by  their  larger  number  in 
the  lymph  leaving  the  gland  as  compared  with  their  num- 
ber in  that  entering  the  gland.  In  a  pathological  condition 
called  leucocythcemia,  which  is  characterized  by  an  enor- 


248      LECTURES   ON    HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

mous  numerical  increase  of  the  leucocytes  in  the  body,  we 
often  find  a  considerable  swelling  of  the  spleen  and  the 
lymphatic  glands — a  fact  which  tends  to  demonstrate  the 
increased  physiological  activity  of  the  organ.  Although 
we  do  not  fully  understand  just  how  and  from  what  mate- 
rials the  leucocytes  are  formed  in  these  organs,  it  cannot  be 
doubted  that  their  production  is  the  result  of  assimilative 
changes  of  materials  supplied  to  these  organs  with  the  blood. 

The  origin  of  the  lymph  ingredients  I  have  already  de- 
scribed in  my  last  lectures. 

The  liver  is  to  be  considered  probably  as  the  organ  in 
which  the  most  important  assimilative  changes  take  place. 
All  the  nutritive  materials  which  are  absorbed  in  the  sto- 
mach and  intestines  by  the  blood-capillaries  are  conveyed 
by  the  portal  vein  through  the  liver. 

The  formation  of  the  bile-pigments  and  bile-salts  in  the 
liver  from  materials  of  the  blood  must  be  considered  as 
synthetical  chemical  processes.  Furthermoi'e,  the  glycoge- 
netic  function  of  the  liver — namely,  the  property  of  the 
cells  of  that  organ  to  transform  materials  of  the  blood  into 
glycogen— is  an  assimilative  function  which  is  of  great  im- 
portance 

Olycogen  is  also  called  animal  starch;  it  is  a  carbohy- 
drate which  is  isomeric  with  starch;  its  chemical  formula 
is  C.HioO,;  with  iodine  it  gives  a  claret-red  color. 

Glycogen  is  formed  in  the  liver  from  the  nutritive  mate- 
rials contained  in  the  blood  of  the  portal  vein.  This  is  de- 
monstrated by  the  fact  that  during  the  stage  of  inanition 
no  glycogen  is  formed  in  the  liver,  whereas  it  is  again  pro- 
duced soon  after  food  is  taken.  Glycogen  is  formed  in  the 
liver  from  albuminous  material,  from  fat,  but  principally 
from  carbohydrates  contained  in  the  blood.  Glycogen  is 
stored  as  such  in  the  liver  cells,  and  only  when  carbohy- 
drates are  needed  in  the  economy  a  quantity  of  the  stored 
glycogen  is  transformed  into  sugar  and  enters  as  such  the 
general  circulation. 


ASSIMILATION.  249 

A  certain  quantity  of  carbohydrate  material  is  constantly 
required  by  the  tissues  for  their  metabolic  processes,  and 
"this  quantity  is  conveyed  to  the  tissues  in  the  form  of 
sugar  in  the  arterial  blood.  Ordinarily  the  quantity  of 
sugar  in  arterial  blood  is  from  0.1  to  0.2  per  cent;  if  it  ex- 
ceeds 0.3  per  cent  it  is  excreted  as  sugar  with  the  urine, 
as  is  observed  in  the  pathological  condition  known  as 
diabetes  mellitus.  The  arterial  blood  derives  its  requisite 
quantity  of  sugar  from  the  glycogen  of  the  liver. 

When  no  carbohydrates  are  taken  with  the  food  the 
liver  forms  the  necessary  quantity  of  glycogen  from  the 
■albuminous  ingredients  and  fat  in  the  blood. 

All  carbohydrates  taken  with  the  food  are  absorbed  as 
sugar;  they  are  conveyed  with  the  blood  of  the  portal 
vein  into  the  liver,  and  her^^  they  are  transformed  into  gly- 
cogen. If  all  sugar  absorbed  in  the  portal  vein  would 
directly  enter  the  general  circulation  there  would  be  an 
undue  increase  of  sugar  in  the  blood,  resulting  in  the  excre- 
tion of  sugar  with  the  urine. 

From  the  foregoing  explanation  it  may  be  said  that  the 
glycogenetic  function  of  the  liver  has  for  its  purpose  the 
regulation  of  the  quantity  of  sugar  in  the  blood. 

It  has  been  found  that  small  quantities  of  glycogen  are 
also  formed  in  muscles  and  other  tissues;  during  the  activ- 
ity of  these  tissues  the  glycogen  in  them  is  transformed 
into  sugar  and  consumed. 

The  fats  which  are  taken  with  the  food  are  absorbed  into 
the  lacteals  and  constitute,  together  with  the  lymph  in  the 
intestinal  lymphatics,  the  chyle.  In  this  form  they  are 
conveyed  into  the  receptaculum  chyli,  and  from  this,  by 
the  thoracic  duct,  into  the  venous  blood.  In  the  blood  the 
fats  disappear  in  about  thirty  hours,  and  it  is  evident  that 
they  are  elaborated,  but  exactly  how  and  where  this  takes 
place  is  not  known.  It  is  believed  that  fat  is  elaborated  to 
some  extent  in  the  lymphatic  glands,  and  that  it  takes  part 
in  the  assimilative  processes  in  these  organs.     The  mate- 


250     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

rials  which  the  tissue  elements  require  for  their  assimila- 
tive processes  are  carried  thither  with  the  arterial  bloody 
but  the  nature  of  the  process  of  the  assimilation  of  these 
materials  into  the  living  protoplasm  of  the  cells  has  not 
been  satisfactorily  explained. 

Many  organs  in  the  body,  such  as  the  thyroid  and  thy- 
mus glands  and  the  suprarenal  capsules,  of  which  we  know 
very  little  as  regards  their  physiological  functions,  are  con- 
sidered as  organs  in  which  important  metabolic  processes 
take  place,  and  the  fact  that  the  extirpation  and  diseases 
of  these  organs  are  often  followed  by  very  marked  systemic 
disturbances  tends  to  demonstrate  their  importance  in  the 
metabolism  of  the  body. 

The  thyroid  gland  is  a  ductless  gland  which  in  structure 
resembles  the  spleen.  The  organ  is  situated  in  front  of 
the  upper  part  of  the  trachea  ;  it  consists  of  two  lobes 
which  are  situated  on  each  side  of  the  trachea,  and  of  a 
transverse  portion  which  connects  the  two  lobes  and  is 
called  the  isthmus.  The  whole  organ  is  surrounded  by  a 
thin  connective-tissue  capsule,  from  which  prolongations 
pass  into  the  organ  and  divide  it  into  compartments; 
these  are  tilled  with  a  brownish-red  substance  which  is 
composed  of  a  dense  capillary  network  enclosing  oval  or 
roundish  bodies  or  vesicles  ;  these  latter  are  lined  with 
cubical  or  columnar  epithelial  cells,  and  are  filled  with  a 
yellowish,  viscid  fluid  in  which  have  been  observed  red 
blood-corpuscles  in  various  stages  of  disintegration.  The 
gland  contains  numerous  lymphatics,  which  surround  the 
vesicles  and  capillaries.  The  contents  of  thelynrphatics  are 
similar  to  those  of  the  vesicles,  and  are  emptied  into  the 
right  lymphatic  duct.  The  thyroid  gland  is  freely  supplied 
with  blood-vessels  and  nerves. 

The  physiological  function  of  the  organ  is,  as  I  have 
stated  before,  not  clearly  understood.  It  is  believed  that 
it  partakes  in  the  formation  of  blood  ingredients.  Ex- 
tirpation  of  the  gland  is   followed   by  tetanus,  epileptic 


ASSIMILATION.  251 

attacks,  etc.  Animals  in  which  the  gland  is  totally  ex- 
tirpated generally  die  soon  after  the  operation.  This  i& 
believed  by  some  to  be  due  to  injuries  of  important  vessels 
and  nerves,  branches  of  which  supply  the  organ;  again 
it  has  been  demonstrated  that  after  a  partial  extirpation 
of  the  gland,  even  if  only  a  small  portion  of  the  organ  is 
left,  no  such  symptoms  follow.  All  these  observations  and 
experiments  tend  to  show  that  the  organ  has  some  connec- 
tion with  important  metabolic  processes  in  the  body. 

A  hypertrophy  of  the  thyroid  gland,  resulting  in  the  for- 
mation of  a  goitre  or  struma,  is  a  pathological  condition 
which  occurs  in  certain  mountainous  districts.  It  is  be- 
lieved that  the  condition  is  caused  by  certain  minerals 
which  are  taken  in  with  the  drinking-water.  Of  late  the 
treatment  of  certain  diseases  with  the  extract  of  the  thy- 
roid gland  has  revealed  satisfactory  results. 

The  thymus  gland  is  a  temporary  organ  ;  at  birth  it 
weighs  about  li  ounces;  it  increases  until  the  second  year, 
and  then  diminishes,  atrophies,  and  becomes  entirely  ob- 
literated at  about  puberty.  The  gland  consists  of  two 
lateral  lobes,  which  are  united  in  the  middle.  The  organ 
is  situated  in  the  thorax  and  neck  ;  in  the  thorax  it  is  con- 
tained in  the  upper  mediastinum  behind  the  sternum  and 
in  front  of  the  pericardium  ;  in  the  neck  it  lies  in  front 
of  the  trachea,  extending  up  to  the  lower  border  of  the 
thyroid  gland.  The  organ  has  a  pinkish  color  and  is  about 
2  inches  long  and  one-half  to  1  inch  wide. 

The  structure  of  the  thymus  gland  resembles  that  of  the 
lymphatic  glands.  It  has  a  fibrous  capsule,  prolongations 
of  which  penetrate  the  organ  and  constitute  its  cortical 
portion,  the  reticulum  of  which  supports  numerous 
lymphoid  cells.  The  medullary  network  consists  of  fine- 
branched  cells  with  more  granular,  cellular,  and  corpuscu- 
lar bodies  in  their  centre.  It  has  been  observed  that  in  the 
medullary  portion  of  the  thymus  gland  there  are  contained 
granular  masses  of  haemoglobin.     The   thymus   gland  is 


^52     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

ductless  ;  it  is  freely  supplied  with  blood-vessels,  nerve- 
fibres,  and  lymphatics.  The  lymph  leaving  the  gland  has 
been  found  to  contain  masses  of  hsemoglobin. 

The  physiological  function  of  the  thymus  gland  is  be- 
lieved by  some  to  be  the  formation  of  the  leucocytes  in 
embryonic  life ;  others  believe  that  the  thymus  gland  is 
the  organ  in  which  in  early  life  the  erythrocytes,  or  the 
haemoglobin  of  these,  originate. 

The  suprarenal  capsules  ^ve  two  oval,  flattened,  yellowish 
bodies  contained  in  the  abdominal  cavity  behind  the  perito- 
neum and  situated  in  front  of  the  upper  part  of  the  kidneys. 

The  structure  of  these  organs  is  somewhat  complex. 
They  are  covered  with  a  fibrous  capsule  which  sends  colum  ■ 
nar  prolongations  perpendicularly  into  the  organ  ;  these 
fibrous  prolongations  contain  n on -striated  muscular  fibres 
and  communicate  by  transverse  fibrous  bands,  thus  form- 
ing a  network  which  in  its  meshes  contains  masses  of 
granular,  nucleated,  many-sided  cells,  and,  between  these, 
fine  lymph-channels.  The  medullary  portion  is  situated 
behind  the  cardiac  portion  thus  described.  The  medullary 
portion  consists  of  a  delicate  stroma  of  connective-tissue 
fibres,  and  in  this  stroma  are  cells  which  resemble  colum- 
nar epithelial  cells.  The  arteries  supplying  the  organ  pene- 
trate and  anastomose  in  its  substance,  and  break  up  into 
a  capillary  plexus  in  the  medullary  portion.  The  organ  is 
supplied  freely  with  lympliatics  and  nerve-fibres. 

The  physiological  function  of  these  organs  is  unknown. 
Some  believe  that  they  play  a  role  in  the  production  of 
the  pigments.  In  a  disease  which  was  first  fully  discussed 
by  Addison,  the  skin  shows  a  peculiar  bronze  discoloration, 
and  it  has  been  found  in  post-mortems  performed  on  pa- 
tients who  died  of  Addison^s  disease  that  the  suprarenal 
capsules  had  undergone  degenerative  changes. 

The  metabolic  processes  in  the  animal  body  depend  upon 
a  proper  supply  of  nutritive  material,  upon  a  proper 
physiological  activity  of  the  tissue  elements,  and  upon  a 


QUESTIONS   AND   EXERCISES.  253: 

proper  circulation.  There  must  be  a  current  which  sup- 
phes  the  nutritive  materials,  and  a  current  which  drains 
off  the  waste  products;  the  latter  are  excreted  by  the- 
excretory  organs. 

During  the  period  of  growth,  development,  and  the  re- 
generation of  tissues  in  the  body  the  assimilative  processes 
are  most  active  and  require  an  increased  supply  of  proper 
nutritive  material.  Almost  all  tissues  and  structures  of  the 
body  possess  in  a  varying  degree  the  power  of  regeneration. 
For  instance,  fractured  bones,  wounds  and  defects  in  tis- 
sues resulting  from  disease  or  surgical  interference,  are 
repaired  owing  to  the  regenerative  processes  which  take 
place  in  the  affected  tissues.  The  process  of  regeneration, 
of  a  tissue  is  the  result  of  the  assimilation  of  materials  of 
the  blood  into  the  histological  elements  of  that  tissue. 

By  the  term  dissimilation  is  meant  the  processes  which, 
take  place  in  the  ingredients  of  the  body  resulting  in  the 
production  of  w^aste  materials.  The  dissimilative  changes 
are  chemical  processes  consisting  in  a  division,  oxidation^ 
and  hydration  of  the  chemical  ingredients  of  the  body. 
The  final  products  of  these  changes  are  urea,  carbon  di- 
oxide, and  water,  and  these  are  excreted  from  the  body. 


QUESTIONS   AND   EXERCISES. 

Subject. — Assimilation. 
Lecture  XXVII. 

553.  What  is  the  nature  of  the  chemical  changes  which 
the  nutritive  materials  undergo  during  their  assimilation 
into  tissue  ingredients  ? 

55i.  Where  are  the  ingredients  of  the  blood  formed  ? 

555.  Where  do  the  lymph  ingredients  originate  ? 

556.  Describe  the  structure  of  the  spleen. 

557.  Give  the  proportion  of  the  white  to  the  red  blood- 


254     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

corpuscles  in  the  blood  of  the  splenic  artery  and  in  that 
of  the  splenic  vein. 

558.  What  is  meant  by  the  giycogenetic  function  of  the 
hver  ? 

559.  Explain  the  purpose  of  the  giycogenetic  function  of 
the  liver. 

560.  What  materials  does  the  liver  transform  into  gly- 
cogen ? 

561.  What  is  glycogen,  its  chemical  formula  and  test  ? 

562.  What  is  diabetes  mellitus  ? 

563.  Describe  in  detail  how  you  would  determine  the 
presence  of  sugar  in  the  urine. 

564.  Describe  the  thyroid  gland.  State  where  it  is  lo- 
cated.    What  is  supposed  to  be  its  physiological  function  ? 

565.  Describe  the  thymus  gland.  State  where  it  is  lo- 
cated.    What  is  supposed  to  be  its  physiological  function  ? 

566.  What  are  the  suprarenal  capsules?  What  is  sup- 
posed to  be  their  physiological  function  ? 

567.  How  is  a  regeneration  of  the  tissues  effected  ? 

568.  What  are  essential  conditions  for  assimilative  pro- 
cesses ? 

569.  What  is  the  nature  of  the  chemical  changes  which 
the  ingredients  of  the  body  undergo  during  dissimilation  ? 

570.  By  what  channels  is  the  nutritive  material  con- 
veyed to  the  tissues,  and  by  what  channels  are  the  pro- 
ducts of  the  dissimilative  processes  of  the  tissues  carried 
off? 

571.  Name  structures  in  the  body  whose  functions  are 
doubtful  or  unknown. 

572.  Define  assimilation. 

573.  What  are  the  functions  of  the  liver  ? 

574.  In  what  manner  are  nutrition  and  repair  carried  on  ? 

575.  What  effects  are  produced  in  the  system  by  removal 
of  the  thyroid  gland  ? 

576.  State  the  source  and  uses  of  the  lymph. 

577.  What  are  the  two  sources  of  income  of  the  body  ? 


LECTURE  XXTLII. 

1.    THE   KIDNEYS   AND   THE    EXCRETION    OF   THE    URINE. 

2.    THE    SUDORIFEROUS    GLANDS   AND    THE 

EXCRETION   OF  3WEAT. 

The  products  of  the  retrogressive  changes  of  the  body  and 
its  ingredients  are  chemical  substances  wliich  when  re- 
tained in  the  organism  produce  serious  disturbances  of  its 
functions.  An  important  function  of  the  animal  organ- 
ism is  the  constant  elimination  of  these  substances.  They 
are  called  the  excrementitious  substances;  carbon  dioxide 
and  urea  are  the  two  principal  mejnbers  of  this  group. 

Carbon  dioxide  is  produced  constantly  in  the  body  as  the 
result  of  the  combustion  of  the  carbon  of  its  organic  in- 
gredients; it  is  eliminated  principally  by  the  process  of 
respiration. 

Urea  is  the  final  product  of  the  oxidation  of  organic 
nitrogenous  ingredients  of  the  body.  The  urea,  and 
a  series  of  organic  nitrogenous  compounds  which  are  in- 
termediary products  of  the  retrogressive  changes  of  the 
organic  nitrogenous  ingredients  of  the  body,  are  eliminated 
largely  in  solution.  These  liquids  are  called  the  excretions. 
The  organs  which  regulate  the  elimination  of  the  excre- 
mentitious substances  are  called  the  excretory  organs. 
The  principal  excretory  organs  of  the  human  body  are  the 
kidneys  and  the  sweat-glands  of  the  skin.  The  liquids  ex- 
creted from  these  organs  also  contain  materials  which  are 
not  excrementitious  substances— for  instance,  water,  inor- 
ganic salts,  etc. ;  these  principally  serve  to  aid  the  process 
of  elimination  and  the  solution  of  excrementitious  sub- 
stances. The  liquids  secreted  by  the  excretory  organs  are 
termed  the  excretions,  in  contradistinction  to  the  liquids 


256     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

secreted  by  other  organs  in  our  body — namely,  liquids  which 
are  intended  to  serve  some  function  in  our  organism;  they 
do  not  contain  excrementitious  substances  as  their  princi- 
pal ingredients,  and  they  are  called  the  secretions.  The 
digestive  juices,  milk,  seminal  fluid,  are  secretions;  the 
urine  and  the  sweat  are  excretions.  A  portion  of  the  ex- 
crementitious substances  is  also  eliminated  with  the  faeces. 

1.   The  Kidneys. 

The  principal  excretory  organs  of  the  human  body  are  the 
kidneys.  These,  two  in  number,  are  situated  in  the  poste- 
rior part  of  the  abdominal  cavity  behind  the  peritoneum,  at 
either  side  of  the  vertebral  column,  in  the  lumbar  region. 
Each  kidney  is  about  4  inches  long,  2i  inches  wide,  and  1  to 
H  inches  thick,  and  weighs  from  -i  to  6  ounces.  A  kidney 
is  bean-shaped  and  directed  with  its  concave  part,  which  is 
termed  the  hilus  of  the  kidney,  toward  the  spinal  column. 
Each  kidney  is  surrounded  and  held  in  its  place  by  3^  fibrous 
ccqjsule,  which  at  the  hilus  is  reflected  upon  the  structures 
which  leave  and  enter  the  organ  at  that  point;  these  are 
the  renal  artery  and  vein,  lymphatics  and  nerves.  The 
excretory  duct  of  the  kidney  is  called  the  ureter.  This  be- 
gins at  the  hilus  from  the  opening  of  the  pelvis  of  the  kid- 
ney; it  then  descends  in  the  abdominal  cavity  and  opens 
into  the  bladder  at  its  lateral  and  posterior  side. 

The  i^elvis  of  the  kidney  is  a  funnel-shaped  excavation 
into  the  organ,  which  at  the  hilus  is  continuous  with  the 
ureter.  The  pelvis  is  divided  into  three  compartments, 
which  are  termed  the  infundihula.  Each  of  these  has  a 
number  of  minor  sacculated  recesses  which  are  called  the 
ccdices  ;  into  these  the  urinif  erous  tubules  pour  their  secre- 
tion. From  the  calices  it  passes  into  the  inf  undibula,  filling^ 
the  pelvis  of  the  kidneys,  from  which  the  urine  flows 
through  the  ureters  into  the  bladder.  The  pelvis  of  the 
kidneys  is  lined  with  transitional  epithelium  which  is  con- 
tinuous with  that  lining  the  bladder  and  ureter. 


THE   KIDXEYS.  257 

The  structure  of  the  kidneys  is  very  comphcated  and  re- 
quires a  thorough  study,  as  only  one  thoroughly  familiar 
with  the  structure  of  these  organs  can  understand  their 
physiological  function. 

The  substance  of  the  kidneys  consists  of  two  structures 
— namely,  the  medullary  and  the  cortical  portion;  the  two 
can  be  plainly  distinguished  with  the  naked  eye  on  a  cross- 
section  of  a  kidney. 

The  inediiUary  portion  consists  of  pyramidal  masses  of  a 
pale-reddish  color.  These  pyramidal  masses  are  called  the 
j)yramids  of  McdpigJii.  They  are  directed  with  their  bases 
toward  the  outer  or  cortical  portion  of  the  organ;  in  each 
of  the  calicos  of  the  latter  is  seen  a  minute  papillary  pro- 
jection, which  is  the  apex  of  one  of  these  pyramids. 

The  cortical  portion  is  darker  red  in  color  and  granular  in 
appearance  ;  it  forms  the  outer  convex  portion  of  the  kidney 
and  fills  the  spaces  left  between  the  pyramids  of  Malpi- 
^hi.  That  portion  of  the  cortical  substance  which  arches 
over  the  bases  of  the  Malpighian  pyramids  is  termed  the 
cortical  arch.  In  it  are  seen,  radiating  from  the  bases  of 
the  Malpighian  pyramids  toward  the  periphery,  light-colored 
pyramidal  columns,  which  are  called  the  pyramids  of  Fer- 
rein.  The  portions  of  cortical  substance  which  are  situated 
between  the  Malpighian  pyramids  are  called  the  columns 
of  Bertin.  The  structures  of  which  the  two  portions  of 
the  kidneys  are  composed  are: 

1.  The  uriniferous  tubules. 

2.  Blood-vessels. 

3.  Lymphatics  and  nerves. 

4.  Connective  tissue  which  holds  these  structures  to- 
gether. 

The  uriniferous  tuhides  are  long  tubes  w^hich  penetrate 
the  substance  of  the  kidney  ;  they  consist  of  a  delicate 
basement  membrane  Avhich  is  lined  with  epithelial  cells  ; 
these  dijffer  in  their  form,  structure,  and  arrangement  in 
the   various    portions    of    the   tubules.     The    uriniferous 

17 


258     LECTURES   ON    HUMAN  PHYSIOLOGY   AND   HISTOLOGY. 


tubules  begin  at  the  cortical  substance  of  the  kidney,  and, 
after  taking  a  very  circuitous  course  through  it,  they  open 
into  the  calices  of  the  pelvis  of  the  organ.  The  peculiar 
appearance  which  the  surface  of  a  cross- section  of  the  kid- 
ney presents— namely,  the  pyramids  of  Malpighi  and  Fer- 
rein — and  the  granular  appearance  of  the  cortical  sub- 
stance, are  produced  by  the  peculiar  and  characteristic 
course  of  the  various  portions  of  the  uriniferous  tubules 

In  their  progress  through  the  substance  of  the  kidney 
the  uriniferous  tubules  frequently  change  their  course.. 
The  diameter  of  a  uriniferous  tubule  is  not  the  same 
throughout,  but  varies  in  different  portions.  These  varia- 
tions in  the  course,  size,  and  epithelial  lining  of  the  urin- 
iferous tubules  are  essential  features  for  the  physiological 
activity  of  the  kidneys. 

A  uriniferous  tubule  is,  for  the  purpose  of  a  better  de- 
scription, divided  into  several  parts.  I  will  first  mention 
their  names  and  respective  diameters,  and  then  describe 
the  course  of  a  uriniferous  tubule  through  the  kidney. 

The  names  of  the  various  portions  of  a  uriniferous- 
tubule  and  their  respective  diameters  are  : 


diameter. 


1.  The  capsule  of  Bowman, 

2.  The  neck, 

3.  The  proximal  convoluted  tubule, 
•Jr.  The  spiral  tube, 

5.  The  looped  tube  of  Henle  ;  this  con- 

sists of  : 

(a)  the  descending  limb, 

(b)  the  looped  portion, 

(c)  the  ascending  limb, 

6.  The  distal  convoluted  tube, 

7.  The  collecting  tube  of  Ballini, 

8.  The  principal  duct, 

9.  The  papillary  duct, 

The  course  of  a  uriniferous  tubule  through  the  substance 


Inch. 

1 
1T3" 

1  00( 
1_ 

Too 
i_ 

"5"0  0 


1 

1 

1  0  (JIT 

1 
10  0  0 

1 
"STTo 

1 
ToTF 

1 
10  0 


THE   KIDNEYS.  259 

of  the  kidney,  and  the  epithehal  hning  of  its  various  por- 
tions, are  as  follows  :  A  uriniferous  tubule  begins  as  a 
round  expansion,  called  the  capsule  of  Bowman,  in  the 
labyrinth — that  is,  in  the  spaces  between  the  pyramids  of 
Ferrein. 

The  capsule  of  Bowman  consists  of  a  delicate  basement 
membrane  which  is  continuous  with  that  of  the  whole 
tubule  ;  the  inner  surface  of  the  capsule  is  lined  with  a 
single  layer  of  flat  epithelial  cells.  The  interior  of  Bow- 
man's capsule  is  partly  filled  by  a  convolution  of  capillary 
blood-vessels  called  the  Malpighiau  tuft  or  glomerulus 
Malpigliii,  and  is  covered  on  its  surface  with  a  single  layer 
of  flat  epithelial  cells  which  are  continuous  with  those 
lining  the  capsule.  The  Malpighian  tuft,  together  with 
the  capsule  of  Bowman  in  which  it  is  contained,  is  called 
a  Malpighian  body. 

At  the  point  where  the  capsule  of  Bowman  joins  the 
proximate  convoluted  tubule  there  is  a  constriction  called 
the  neck.  The  tube  then  widens  again  and  passes  in  a  tor- 
tuous course  downward  between  the  pyramids  of  Ferrein. 
This  portion  is  termed  the  proximal  convoluted  tubule ; 
the  interior  of  this  is  lined  with  a  single  layer  of  columnar 
or  polyhedral  epithelial  cells  ;  the  protoplasm  of  these  is 
more  homogeneous  and  cloudy  in  that  part  which  is  directed 
toward  the  lumen,  whereas  the  part  toward  the  basement 
membrane  is  more  striated  ;  the  striee  diverge  toward  the 
basement  membrane,  giving  to  that  part  of  the  protoplasm 
a  brush-like  appearance  ;  the  protoplasm  contains  a  round 
nucleus  which  is  situated  near  the  free  surface  of  the  cell ; 
during  activity  the  border  of  these  cells  is  also  striated. 
The  next  portion  of  the  uriniferous  tubule  is  the  sp)iral 
tube.  It  is  spiral-shaped,  as  the  name  implies;  it  is  a  little 
narrower  in  diameter  than  the  previous  portion,  and  is 
Uned  with  epithelial  cells  similar  in  structure  to  those  lin- 
ing the  convoluted  tubule. 

The  uriniferous  tubule  now  enters  the  Malpighian  pyra- 


260     LECTURES  ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY". 

mid,  its  diameter  suddenly  narrows,  and,  after  a  straight 
descent  in  the  pyramid  ahiiost  to  its  apex,  it  turns  and 
passes  straight  up.  This  portion  of  the  uriniferous  tubule 
is  called  the  looped  tube  of  Henle;  it  consi^i^ots,  descending 
limb,  a  loop,  and  aii  ascending  limb.  The  descending  limb 
is  the  portion  which  passes  downward  in  the  Malpighian 
pyramid;  this  portion  is  narrow  in  diameter  and  is  lined 
with  a  single  layer  of  flattened,  elongated,  and  nucleated 
cells.  The  loojjed  portion  of  Henle's  tube  has  again  a  wider 
diameter  and  is  lined  with  short  columnar  cells.  The  as- 
cending limb  of  Henle's  tube  is  of  the  same  diameter  as  the 
loop  and  is  lined  with  the  same  epithelium;  in  its  upper 
portion  this  ascending  limb  has  a  slightly  spiral  course. 
This  portion  of  the  tube  passes  upward  to  the  base  of  the 
pyramid  and  on  to  the  pyramid  of  Ferrein,  where  it  widens 
and  becomes  the  convoluted  tube.  As  the  tube  again  re- 
enters the  cortical  portion  at  the  base  of  the  pyramid  of 
Ferrein  it  widens  and  becomes  convoluted,  and  is  called  the 
distal  convoluted  tubule.  This  portion  is  wide  and  has  the 
same  diameter  as  the  proximal  convoluted  tubule;  it  is  also 
lined  with  short  columnar  epithelium,  and  passes  in  a  tor- 
tuous course  through  the  cortical  portion  beneath  the  cap- 
sule of  the  kidney.  The  uriniferous  tubule  now  re-enters 
the  pyramid  of  Ferrein;  it  becomes  a  little  narrower  and 
passes  down  in  the  pyramid  of  Ferrein  and  in  the  Malpighian 
pyramid  almost  to  its  apex;  this  portion  of  the  tube  is  called 
the  straight  or  collecting  tube  of  Bellini;  it  is  also  lined  with 
columnar  epithelium.  Near  the  apex  of  the  Malpighian 
pyramid  a  number  of  such  collecting  tubes  join  and  form 
a  short  tube,  the  principal  tube,  and  again  several  of  these 
open  into  one  tube,  called  the  papillary  duct;  from  200  to 
300  of  these  open  at  the  surface  of  a  papilla  which  is 
formed  by  the  projection  of  the  apex  of  a  Malpighian  pyra- 
mid into  the  calices  of  the  infundibula. 

The  various  names  used  in  describing  the  tubular  system 
of  the  kidney  merely  designate  the  various  portions  of  one 


THE   KIDNEYS.  261 

long,  continuous  tubule— namely,  a  uriniferous  tubule 
which  passes  through  the  substance  of  the  kidney,  often 
changing  its  course  and  diameter. 

The  epithehal  cells  lining  the  uriniferous  tubule  consti- 
tute the  pare;ic%»ia  of  the  kidney;  these  cells  are  of  the 
short  columnar  variety  in  all  portions  of  the  uriniferous 
tubule,  with  the  exception  of  those  lining  the  capsule  of 
Bowman  and  the  descending  limb  of  Henle's  looped  tube, 
which  are  of  a  flat  variety.  It  is  of  great  importance  for 
the  understanding  of  the  physiological  function  of  the 
kidney  to  remember  the  varying  diameters  of  the  several 
portions  of  the  uriniferous  tubules,  particularly  the  sud- 
den narrowing  of  the  neck  and  the  descending  limb  of 
Henle's  tube. 

The  arraQgement  of  the  blood-vessels  in  the  kidneys  is 
also  complicated  and  characteristic.  The  kidneys  are  sup- 
plied with  blood  by  a  branch  of  the  abdominal  aorta  called 
the  renal  artery;  this  enters  the  kidney  at  the  hilus  and 
gives  off  branches  which  pass  into  the  columns  of  Bertin 
— viz.,  the  masses  of  cortical  substance  between  the  Mal- 
pighian  pyramids;  these  branches  pass  up  along  the  sides 
of  the  Malpighian  pyramids  and  then  arch  over  their 
bases;  they  are  called  the  arterial  arcade.  From  these,  two 
sets  of  arterioles  are  given  off— namely,  the  artericB  rectce 
and  the  interlobular  arteries.  The  arterise  rectse  are  small 
arterioles  which  pass  straight  down  in  the  Malpighian 
pyramids  and  form  capillary  loops  which  surround  the 
uriniferous  tubules.  The  interlobular  arteries  are  small 
arterioles  which  pass  straight  upward  in  the  pyramids  of 
Ferrein  and  give  off  branches  which  pass  into  the  cortical 
substance,  where  one  such  arteriole  enters  each  capsule  of 
Bowman  and  breaks  up  into  a  capillary  plexus  known  as 
the  Malpighian  tuft.  From  this  another  arteriole  is  formed, 
which  passes  out  of  Bowman's  capsule  opposite  the  point 
where  the  afferent  arteriole  enters  the  capsule;  the  afferent 
arteriole,  immediately  after  leaving  the  capsule,  breaks  up 


262    LECTURES   ON  HCMAN   PHYSIOLOGY   AXD    HISTOLOGY. 

into  a   secondary  capillary   plexus   which  surrounds  and 
supplies  the  uriniferous  tubules  in  the  cortical  portion. 

The  veins  of  the  kidneys  arise  (a)  from  numerous  small 
venous  plexuses  which  are  situated  directly  beneath  the 
capsule  of  the  kidney  and  are  described  as  the  stars  of 
Verhayen;  (b)  from  the  capillary  plexus  which  surrounds 
the  uriniferous  tubules  in  the  cortical  portion;  and  (c)  from 
the  capillary  plexus  which  surrounds  the  uriniferous  tu- 
bule in  the  Malpighian  pyramids. 

The  venules  arising  from  the  stars  of  Verhayen,  and 
those  arising  from  the  capillary  plexuses  surrounding  the 
uriniferous  tubules  in  the  cortical  portion,  form  the  tute?^- 
lohular  veins  which  open  into  the  venous  arcades.  The 
venules  arising  from  the  capillary  plexuses  surrounding  the 
uriniferous  tubules  in  the  pyramids  of  Malpighi  form  the 
vence  rectce ;  these  ascend  in  the  pyramids,  and  at  their 
bases  open  into  the  venous  arcade. 

The  venous  arcade  surrounds  the  Malpighian  pyramids, 
like  the  arterial  arcade,  and  passes  down  between  the 
Malpighian  pyramids,  forming  branches  which  unite  and 
form  the  i^eual  vein,  which  leaves  the  kidneys  at  the 
hilus. 

The  peculiarities  and  characteristics  of  the  blood  circula- 
tion— particularly  of  the  arterial — in  the  kidneys  consist, 
first,  in  that  each  portion  receives  a  separate  blood-supply, 
as  it  were,  by  direct  branches  from  the  arterial  arcade,  and, 
secondly,  in  that  the  interlobular  arterioles  break  up  into  a 
secondary  capillary  plexus  after  leaving  Bowman's  cap- 
sule. This  arrangement  of  the  circulatory  system  of  the 
kidneys  is  an  important  factor  in  the  physiological  activity 
of  these  organs. 

The  lymphatics  of  the  kidneys  begin  by  minute  channels 
in  the  parenchyma  and  from  lymph-spaces  beneath  the 
capsule  of  the  organ.  The  lymph-vessels  pass  out  at  the 
hilus  and  communicate  with  the  lumbar  lymphatic  glands. 

The  nerves   of  the  kidneys  are  derived  from  the  i-enal 


THE   URINE.  263 

plexus,  the  fibres  being  principally  distributed  to  the  walls 
of  the  blood-vessels. 

The  Urine. 

The  excretion  of  the  kidneys  is  called  the  urine.  Nor- 
mal human  urine  is  generally  a  clear  liquid  which  has  a 
pale-yellowish  color;  if  the  urine  is  concentrated  its  color 
is  darker,  even  reddish.  In  many  pathological  conditions 
the  color  of  the  urine  is  altered  by  the  admixture  of  blood, 
pus,  bile,  etc.  The  taking  of  certain  drugs  often  influ- 
ences the  color  of  the  urine,  as,  for  instance,  senna  pro- 
duces an  intense  red,  rhubarb  a  brown,  and  carbolic  acid  a 
black  discoloration. 

The  reaction  of  urine  is  generally  acid.  This  is  not  due 
to  the  presence  of  a  free  acid,  but  to  the  presence  of  sodium 
sulphate.  The  acidity  of  urine  is  increased  by  the  taking 
of  acids,  and  it  is  decreased  by  the  taking  of  alkalies  ;  also 
during  the  process  of  digestion,  and  in  pathological  condi- 
tions when  the  urine  becomes  mixed  with  pus,  as  it  is  in 
the  case  of  pyelitis,  cystitis,  etc. 

The  specific  gravity  of  urine  is  subject  to  variations  ;  it 
is  generally  between  1010  and  1020  ;  it  depends  upon  the 
quantity  of  dissolved  solids.  Normally  it  is  increased,  there- 
fore, after  the  taking  of  heavy  meals,  and  when  the  urine 
is  concentrated,  as  it  is  when  long  retained  in  the  bladder 
owing  to  the  reabsorption  of  water  by  the  epithelial  lining 
of  the  bladder.  The  specific  gravity  is  decreased  after 
drinking  large  quantities  of  water.  The  specific  gravity  is 
influenced  by  many  pathological  conditions  :  it  is  increased 
in  fevers,  diabetes  mellitus,  etc.,  and  decreased  in  the  con- 
dition known  as  polyuria. 

Normal  human  urine  has  a  characteristic  peculiar  aro- 
matic odor,  which  is  also  often  altered  in  pathological 
conditions  and  when  certain  drugs  have  been  taken. 

The  chemical  composition  of  normal  human  urine  is  as 
follows  : 


264     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

It  contains  about  96  per  cent  of  water  and  4  per  cent  of 
solids  ;  the  latter  are  contained  in  the  urine  principally  ia 
solution,  and  are  (a)  organic  and  (b)  inorganic  substances. 
(a)  The  organic  ingredients  are  : 

Urea. 

Uric  acid  and  hippuric  acid. 

Oxalic  acid. 

Oxaluric  acid. 

Kreatinin. 

Xanthin. 

Sarkin. 

Coloring  substances. 

Indican. 

Phenol. 

Ferments. 

Mucus. 
(6)  The  inorganic  ingredients  are  :     Sodium  and  potas- 
sium chloride,  sodium  sulphate,  and  phosphates  and   sul- 
phates of  lime  and  magnesia. 

Urea  is  the  final  product  of  the  oxidation  of  the  nitro- 
genous substances  in  the  body.  The  chemical  formula  of 
urea  is  C0(NH„)2 ;  it  is  an  organic  nitrogenous  substance 
composed  of  CO,  +  (NH,)„  —  H^O.  It  crystallizes  in  color- 
less, glistening,  quadrangular  prisms  and  in  needles  ;  the 
crystals  are  neutral  in  reaction,  taste  bitter,  and  are  freely 
soluble  in  water  and  in  alcohol,  but  insoluble  in  ether. 

Normal  human  urine  contains  from  2^  to  3  per  cent  of 
urea.  A  healthy  adult  man  excretes  about  30  to  40  grammes 
of  urea  with  the  urine  in  twenty-four  hours;  this  quantity 
is  increased  when  food  rich  in  nitrogenous  substances  is 
taken,  and  is  decreased  when  a  small  amount  or  no  albu- 
minous material  is  taken  with  the  food.  The  quantity  of 
urea  in  the  urine  varies  at  different  periods  of  the  day, 
and  is  influenced  by  many  other  conditions.  It  is  increased 
by  muscular  exercise,  decreased  by  rest  and  fasting;  it  is 
highest  several  hours  after  a  meal. 


THE   URINE.  265- 

Increased  dissimilative  changes  in  nitrogenous  tissue  in- 
gredients increase  the  quantity  of  urea  in  tlie  urine;  such 
is  the  case  in  febrile  conditions  and  in  chronic  wasting- 
diseases. 

Urea  is  also  found  in  small  quantities  in  the  blood,  lymph, 
chyle,  bile,  in  the  liver,  spleen,  brain,  lymphatic  glands,  etc. 

The  liver  is  believed  to  be  the  organ  in  which  the  urea  is 
formed;  experiments  made  on  animals  tend  to  sustain 
this  theory. 

The  two  sources  of  the  urea  in  the  animal  body  are: 
1.  The  organic  nitrogenous  food  ingredients.  2.  The  de- 
generative processes  of  the  nitrogenous  tissue  ingredients. 

Uric  acid  is  also  an  organic  nitrogenous  substance;  its 
chemical  formula  is  C^H.N.Oj;  it  crystallizes  in  rhombic 
plates,  is  odorless,  colorless,  and  tasteless,  and  but  slightly 
soluble  in  water.  In  the  human  urine  it  is  generally 
found  in  the  form  of  urates  of  sodium  and  potassium, 
which  are  soluble  in  water.  The  quantity  of  uric  acid  ex- 
creted in  twenty-four  hours  is  about  0.5  to  2  grammes. 
The  source  of  uric  acid  is  probably  the  same  as  that  of 
urea,  as  it  is  proportionally  increased  and  decreased  with 
this.  It  has  been  observed  that  the  quantity  of  uric  acid 
is  increased  in  pathological  conditions  where  there  is  a 
disintegration  of  the  leucocytes. 

The  other  orgaiiic  nitrogenous  ingredients  mentioned  are 
all  products  of  the  retrogressive  changes  of  nitrogenous 
substances  in  the  body;  they  are  all  present,  but  in  small 
quantities,  and  often  only  accidental  ingredients.  Hippu- 
ric  acid  is  the  chief  product  of  the  retrograde  changes  of 
the  nitrogenous  ingredients  in  the  herbivora;  in  human 
urine  it  is  also  found,  but  only  in  small  quantities. 

The  coloring  substances  of  human  urine  are  urobilin  and 
urochrome ;  they  are  organic  nitrogenous  substances  de- 
rived from  the  bile-pigments. 

Indican  s^ndi phenol  are  two  substances  which  are  products 
formed  during  the  pancreatic  digestion  of  nitrogenous  food. 


266     LECTURES   ON   HUMAN  PHYSIOLOGY   AND    HISTOLOGY. 

It  has  been  demonstrated  that  urine  contains  ferments 
which  have  a  r>hght  diastatic  and  peptic  action;  the  exact 
nature  of  these  ferments  is  not  understood.  Urine  often 
contains  traces  of  sugar,  especially  so  after  the  taking  of 
foods  or  drinks  containing  sugar. 

The  small  quantity  of  mucus  which  urine  contains  is 
secreted  by  the  cells  and  glandular  organs  contained  in  the 
mucous  membrane  of  the  urinary  tract. 

The  inorganic  solid  ingredients  of  the  urine  are  princi- 
pally the  salts  w^hich  are  taken  in  with  the  food;  the  prin- 
cipal one  is  sodium  chloride. 

The  phosphates  and  sulphates  are  to  some  extent  also 
formed  during  the  decomposition  of  the  organic  nitroge- 
nous substances  of  the  body. 

The  carbonates  are  largely  formed  from  the  CO^  which 
is  the  product  of  the  oxidation  of  the  carbon  of  the  organic 
ingredients  and  materials  in  the  body.  Urine  contains  a 
considerable  quantity  of  free  CO^. 

The  urine  of  the  herbivora  contains  more  carbonates  in 
proportion  than  sulphates  and  phosphates,  and  is  therefore 
generally  alkaline;  this  abundance  of  carbonates  is  due  to 
the  union  of  CO^  with  the  potassium  salts  of  the  herbs  and 
fruits. 

The  water  of  the  urine  is  the  excess  contained  in  the 
tissues  and  in  the  blood.  Such  excess  interferes  with  the 
metabolic  processes  of  the  organism  and  is  therefore 
eliminated;  this  is  clearly  shown  by  the  increase  of  water 
in  the  urine  following  the  drinking  of  large  quantities  of 
liquids. 

The  quantity  and  quality  of  the  ingredients  are  deter- 
mined by  chemical  tests.  You  will  learn  this  in  your  prac- 
tical course  in  urinalysis. 


LECTUEE   XX J  X. 

THE   EXCRETIOX   OF   URIXE. 

-  The  physiological  process  of  the  excretion  of  the  urine. 
and  the  mechanism  connected  with  it.  have  been  the  subject 
of  much  study  and  discussion,  and  many  valuable  observa- 
tions and  experiments  in  this  direction  have  been  made  by 
men  such  as  Bowman,  Luchuig,  Heideuhain.  yussbaum, 
and  many  others,  and  various  theories  as  to  the  exact  de- 
tails have  been  advanced.  The  results  of  the  many  obser- 
vations and  experiments  on  the  subject  may  be  summed 
up  as  follows  : 

1.  The  urine  is  formed  in  the  kidneys,  but  the  larger 
portion  of  the  principal  excrementitious  substances  con- 
tained in  it  are  not  formed  in  the  kidneys  ;  they  are  formed 
in  the  tissues  and  organs  of  the  body,  are  taken  up  by  the 
blood,  and  excreted  from  it  by  the  kidneys. 

2.  A  small  quantity  of  the  ingredients  of  the  urine  is 
formed  in  the  kidneys  as  the  product  of  chemical  processes 
in  them  :  this  applies,  for  instance,  to  some  of  the  salts 
which  cause  the  acidity  of  the  urine. 

3.  The  processes  which  effect  the  excretion  of  the  urine 
are:  (a)  filtration,  (b)  osmosis,  (c)  the  vital  property  of  the 
epithelial  cells  lining  the  uriniferous  tubules. 

4.  The  water  of  the  urine,  and  some  of  its  more  easily 
diffusible  ingredients,  such  as  salts,  are  excreted  from  the 
blood  in  the  capillary  plexus — viz.,  the  glomerulus  in  the 
Malpighian  bodies — by  a  process  of  filtration  catised  by  the 
pressure  of  the  blood  in  this  plexus. 

5.  The  solid  ingredients  of  the  urine  are,  to  the  greatest 
extent,  excreted  in  the  convoluted  portions  of  the  urinifer- 


268     LECTURES   ON   HU.MAN   PHYSIOLOGY   AND   HISTOLOGY. 

ous  tubules  from  the  blood  in  the  capillary  plexus  sur- 
rounding it. 

The  principal  ingredients  of  the  urine  are  not  formed  in 
the  kidneys,  but  in  the  tissues  and  organs  of  the  body, 
from  which  they  are  taken  up  by  the  blood.  This  is  shown 
by  facts.  Most  of  the  ingredients  of  the  urine — for  in- 
stance, urea — are  found  in  the  blood  as  such  in  small 
quantities  ;  these  rapidly  increase  and  accumulate,  pro- 
ducing convulsions,  coma,  and  death  whenever  their  elimi- 
nation is  interfered  with,  as,  for  instance,  in  certain  patho- 
logical structural  changes  in  the  kidneys.  The  same  result 
is  obtained  when  the  renal  arteries  are  tied  or  when  the 
kidneys  are  extirpated. 

The  excretion  of  the  water  of  the  urine  is  believed  to 
take  place  principally  in  the  Malpighian  bodies  of  the  urin- 
iferous  tubules  by  a  process  of  filtration.*  The  Malpighian 
body  has  the  essential  structure  of  a  filter.  The  glomeru- 
lus or  primary  capillary  plexus  of  the  renal  artery  is  the 
membrane  through  which  the  filtration  takes  place.  The 
blood  in  this  capillary  plexus  is  the  fluid  to  be  filtered  ;  to 
effect  this  it  must  be  subjected  to  a  certain  pressure.  The 
blood-pressure  in  this  capillary  plexus  is  greater  than  in 
other  capillaries,  because  the  afferent  vessel  which  conveys 
the  blood  into  the  plexus  is  greater  than  the  efferent 
vessel  which  carries  the  blood  off  from  the  plexus,  and, 
furthermore,  because  the  current  of  blood  from  this  plexus 
meets  a  further  resistance  in  the  secondary  capillary  plexus 
of  the  renal  artery — namely,  the  plexus  which  surrounds 
the  tubular  portions  of  the  uriniferous  tubule.  The  cavity 
into  which  the  fluid  is  filtered  is  the  space  between  the 
outer  surface  of  the  glomerulus  and  the  inner  surface  of 
the  capsule  of  Bowman  ;  this  cavity  is  lined  by  a  single 
layer  of  fiat  epithelial  cells.  By  this  process  of  filtration 
not  only  water,  but  also  some  of  the  more  easily  diffusible 
ingredients  of  the  urine— for  instance,  salts— are  excreted 
from  the  blood.     This  excretion,  however,  cannot  be  con- 


THE   EXCRETION   OF   URINE.  269 

siderecl  as  produced  alone  by  filtration,  as  such  a  process 
would  also  cause  certain  substances   of   the  blood  which 
normally  are  not  found  in  the  urine  to  pass  through  the 
capillary  walls.     The  small  degree  of  diffusibility  of  many 
of  the   blood  ingredients — for  instance,    albumin — cannot 
be  considered  as  the  reason  for  their  not  filtering  through 
the  walls   of   the    capillaries  of   the  glomerulus  together 
with  the    water  and    other  substances,    because,    in   the 
pathological  structural  conditions  in  which  the  epithelial 
lining  of  the  Malpighian  bodies  is  destroyed,  albumin  and 
other  substances   which   normally  are   not   found  in  the 
urine  are  filtered  through  the  walls  of  the  capillaries  into 
the  uriniferous  tubules,  even  if  the  blood-pressure  in  the 
renal  artery  is  not  increased.    It  is  believed  that  the  special 
vital  property  of  the  epithelial  cells  lining  the  uriniferous 
tubule  consists  in  their  possessing  a  special  affinity  for  cer- 
tain ingredients  of  the  blood — namely,  the  normal  ingre- 
dients of  the  urine  ;  they  thus  favor  the  excretion  of  these 
substances  and  to  some  extent   prevent  the  excretion  of 
others.     This  special  vital  property  of  the  epithelial  cells 
must  therefore  be  considered  as  an  important  factor  in  the 
mechanism  of  the  excretion  of  urine.     It  has  been  deuion- 
strated  by  experiments  that  the  largest  portion  of  the  solid 
ingredients  of  the  urine  is  excreted  by  the  epithelial  cells 
lining  the  convoluted  portions  of  the  uriniferous  tubules, 
from  the  blood  in  the  capillary  plexus  surrounding  them. 
The  process  of  excretion  in  this  part  of  the  tubule  is  not 
effected  by  a  filtration,  but  by  the  physiological  activity  of 
the  epithelial  lining,  and  it  is  believed  that  the  excretion  of 
substances  in  this  part  of  the  uriniferous  tubule  is  to  some 
■extent  effected  by  osmosis.     That  the  solid  ingredients  of 
the  urine  are  principally  excreted  in  this  part  of  the   urin- 
iferous tubule  is  proved  by  the  following  experiment  :  If  a 
solution  of   sodium  sulpho-indigotate  is  injected  into  the 
blood  the  eliminated  urine  will  soon  show  a  deep-blue  dis- 
coloration ;  this  is  due  to  the  fact  that  the  particles  of  the 


270     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

sodium  sulpho-indigotate  are  excreted  by  the  kidneys. 
If  during  this  process  a  kidney  is  extirpated  and  examined 
it  will  be  found  that  the  structures  which  are  formed  by 
the  convoluted  tubules  are  stained  blue,  whereas  the  other 
parts  are  not  stained  at  all.  If  examined  microscopically 
it  will  be  found  that  this  is  due  to  the  presence  of  the  par- 
ticles of  the  staining  materials  in  the  protoplasm  of  the 
epithelial  cells  lining  the  convoluted  tubules,  whereas  the 
cells  lining  the  other  portions  of  the  uriniferous  tubules  do 
not  contain  any  such  particles.  The  peculiar  structure  of 
the  epithelial  cells  lining  the  convoluted  tubules,  and  the 
change  observed  in  these  cells  during  their  activity,  also 
tend  to  sustain  the  theory  that  they  excrete  the  solid  in- 
gredients of  the  urine. 

That  the  excretion  of  substances  in  this  part  of  the  urin- 
iferous tubules  is  not  produced  by  a  filtration  is  evident, 
because  the  pressure  of  the  blood  in  the  capillary  plexus 
surrounding  this  portion  of  the  tubes  is  not  greater  than 
in  any  other  capillaries.  The  pressure  is  not  sufficient  to- 
cause  a  filtration,  because  the  urine  in  the  convoluted 
tubule  has  a  tension  sufficient  to  prevent  a  filtration  of 
substances  from  the  blood  through  the  capillaries  into  the 
convoluted  tube.  The  tension  of  the  urine  in  the  convo- 
luted tube  is  maintained  by  the  small  calibre  of  the  straight 
portions  of  the  uriniferous  tubules,  which  permits  only  a 
slow  and  gradual  flow  of  the  urine  in  the  convoluted 
tubule. 

The  normal  urine  contains  a  greater  proportion  of  urea 
and  other  solid  ingredients  than  the  blood. 

Taking  into  consideration  the  fact  that  in  the  Malpi- 
ghian  bodies  only  a  comparatively  small  quantity  is  filtered 
through  the  glomerulus  together  with  the  water,  it  follows 
that  urine  passing  from  Bowman's  capsule  into  the  convo- 
luted tubule  is  a  very  dilute  solution  of  solids  in  water.  In 
the  convoluted  tubule  the  urine  becomes  more  concentrated, 
owing  to  the  admixture  with  the  particles  of  solid  ingre- 


THE   EXCRETION   OF   URIXE.  271 

dients  excreted  by  the  epithelial  cells.  The  exact  nature 
of  the  excretion  of  the  substances  by  these  cells  is  not  fully 
understood,  but  it  is  likely  that  they  possess  a  special  af- 
finity for  the  substances  which  are  formed  as  ingredients 
of  normal  urine.  It  is  believed  that  there  takes  place  an 
osmotic  current  between  substances  in  the  blood  of  the 
capillary  plexus  surrounding  the  convoluted  tubules  and 
substances  of  the  urine  in  the  convoluted  tubules,  and 
that  during  this  osmotic  current  certain  ingredients  of  the 
blood  having  comparatively  high  endosmotic  equivalents 
are  exchanged  for  a  quantity  of  water  of  the  urine  in  the 
convoluted  tubule.  This  osmotic  current  is  aided  by  the 
slow  flow  of  the  urine  from  the  convoluted  tubules  through 
the  narrow,  straight  portions  of  the  uriniferous  tubules. 
This  also  explains  the  greater  degree  of  concentration  of 
the  urine  in  the  convoluted  tubule  as  compared  with  that 
formed  in  Bowman's  capsule.  The  passing  of  the  solid 
matter  through  the  epithelial  cells  lining  the  convoluted 
tubules  is  believed  to  be  produced  in  a  manner  similar  to 
the  passing  of  the  particles  of  fat  into  the  lacteals  through 
the  epithelial  cells  covering  the  villi — namely,  by  motions 
of  the  protoplasm  of  these  ceUs. 

The  Quantity  of  Urine  Excreted;  Conditions  Influencing  If. 

The  quantity  of  urine  excreted  in  twenty-four  hours  by 
the  healthy  adult  is  subject  to  very  great  variations;  1,500 
cubic  centimetres  is  about  the  average. 

The  excretion  of  urine  is  increased: 

1.  By  all  conditions  which  increase  the  general  blood- 
pressure;  for  instance,  increased  cardiac  action,  contrac- 
tion of  blood-vessels  (general  or  local),  obstructions  to 
venous  flow,  etc. 

2.  By  drinking  large  quantities  of  liquids,  and  the  conse- 
quent tendency  of  the  system  to  eliminate  the  superfluous 
water,  which  retards  the  metabolic  processes. 

3.  By  a  contraction   of  the   blood-vessels   of   the   skin, 


273      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

which  retards  the  ehmiiiatioii  of  water  from  the  surface  of 
the  body,  as  is  the  case  in  cold  weather. 

4.  By  taking  foods  rich  in  nitrogenous  materials. 

5.  By  the  use  of  diuretics  These  are  drugs  which,  by 
their  effect  on  the  circulatory  system,  increase  the  excre- 
tion of  urine. 

The  excretion  of  urine  is  decreased: 

1.  By  all  conditions  which  decrease  the  general  blood- 
pressure. 

2.  By  large  hemori'hages,  sweats,  and  diarrhoeas. 

3.  By  fasting  and  when  small  quantities  of  liquids  are 
taken. 

4.  When  foods  containing  small  quantities  of  nitroge- 
nous materials  are  taken. 

5.  In  warm  weather,  when  the  vessels  of  the  skin  are 
dilated,  thus  favoring  the  elimination  of  water  from  the 
skin. 

The  quantity  of  urine  depends  upon  the  quantity  of 
water  excreted  by  the  kidneys,  and  is  therefore  influenced 
principally  by  the  blood-pressure,  and  consequently  by  all 
the  conditions  which  influence  the  blood-pressure.  The 
quantity  of  solids  in  the  urine  depe-nds  upon  the  taking  of 
such  foods  as  produce  their  formation,  upon  the  metabol- 
ism of  the  tissues,  and  upon  the  excretory  activity  of  the 
epithelial  cells  lining  the  uriniferous  tubules.  The  presence 
of  abnormal  ingredients  in  the  urine  is  often  due  to  patho- 
logical lesions,  as,  for  instance,  the  presence  of  sugar  in 
diabetes  mellitus,  or  the  increase  of  phosphates  in  nervous 
diseases,  etc.  Sometimes  an  increase  in  the  blood-pressure 
is  the  cause  of  the  presence  of  abnormal  ingredients  in  the 
urine,  as,  for  instance,  the  presence  of  albumin  in  cardiac 
diseases;  and,  lastly,  structural  changes  in  the  kidneys 
must  be  mentioned  as  a  frequent  cause  of  the  presence  of 
abnormal  ingredients  in  the  urine. 

The  quantity  of  urine  excreted  at  the  various  periods  of 
the  day  also  varies.     At   night   it    is  at   its  minimum;  it 


THE   EXCKETION   OF   URINE.  273 

increases  in  the  forenoon,  reaches  its  maximum  two  to  three 
hours  after  the  main  meal,  and  gradually  decreases  again 
toward  night.  The  quantity  is  influenced  by  the  quantity 
of  liquids  and  kinds  of  food  taken,  by  the  temperature  and 
physical  activity  during  the  various  periods  of  the  day. 
The  excretory  activity  of  the  kidneys  is  continuous.  The 
-activity  of  both  kidneys  is  not  equal  at  all  times.  It  has 
been  observed  that  when  one  kidney  is  extirpated  the  other 
will  assume  the  excretory  activity  for  both. 

The  Nerve  Influence  on  the  Excretory  Function  of  the 

Kidneys. 

The  excretory  function  of  the  kidneys  is  principally  in- 
fluenced and  regulated  by  the  vasomotor  nerve-fibres, 
which  arise  from  a  special  nerve-centre  located  in  the 
floor  of  the  fourth  ventricle  of  the  brain. 

The  fibres  arising  from  this  centre  pass  down  in  the 
spinal  cord  to  the  renal  plexus  and  are  distributed  from  it 
to  the  kidneys,  terminating  in  the  walls  of  the  blood-ves- 
sels. Injury  to  the  vasomotor  centre  of  the  vascular  sys- 
tem of  the  kidneys  causes  a  dilatation  of  the  blood-vessels 
of  the  same  and  a  consequently  increased  excretion ;  sec- 
tion of  the  renal  plexus  has  the  same  effect. 

Paralysis  of  the  vasomotor  nerves  of  a  large  portion  of 
the  body  causes  a  decrease  in  the  excretion  of  urine.  This 
results  from  a  decreased  blood  pressure  in  the  renal  vessels, 
caused  by  a  dilatation  of  the  walls  of  the  blood-vessels,  the 
vasomotor  nerves  of  which  have  been  paralyzed.  The 
presence  of  special  secretory  nerve-fibres  in  the  kidneys 
has  not  been  demonstrated. 

The  Evacuation  of  Urine. 

The  urine,  which  is  constantly  secreted  by  the  kidneys, 
passes  through  the  ureters  into  the  urinary  bladder.  The 
ureters  are  the  excretory  ducts  of  the  kidneys. 

The  ureter  begins  as  a  funnel-shaped  expansion  at  the 

18 


274    LECTURES    ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

hilus  of  the  kidney;  it  gradually  becomes  a  cylindrical 
tube  of  the  size  of  a  goose-quill,  which  passes  obliquely 
downward  and  inward  through  the  abdominal  cavity  into 
the  pelvis,  where  it  opens  into  the  bladder  at  its  base. 

A  ureter  consists  of  a  fibrous,  a  muscular,  and  a  mucous 
coat;  the  latter  is  lined  by  transitional  epithelium.  The 
muscular  coat  consists  of  circular  and  muscular  fibres. 

The  urinary  bladder  is  a  musculo  membranous  sac;  it  is 
located  in  the  pelvic  cavity  behind  the  pubes  and  in  front 
of  the  rectum.  The  bladder  serves  as  a  reservoir  for  the 
urine;  it  is  about  five  inches  long  and  three  inches  wide^ 
and  holds  about  one  pint. 

The  bladder  consists  of  an  upper  portion,  the  apex,  a 
middle  portion,  the  body,  and  a  lower  portion,  the  base  or 
fundus.  The  organ  is  suspended  by  a  fibrous  band,  the 
urachus,  which  passes  from  the  apex  of  the  bladder  to  the 
umbilicus.  The  posterior  surface  of  the  bladder  is  covered 
with  peritoneum;  the  anterior  and  lateral  sides  have  no 
serous  covering.  The  anterior  part  of  the  base  of  the 
bladder  is  at  one  point  somewhat  constricted;  this  is  called 
the  neck,  and  is  the  commencement  of  the  urethra.  The 
bladder  is  composed  of  four  coats — namely,  serous,  mus- 
cular,  submucous,   and  mucous. 

The  serous  coat  is  derived  from  the  peritoneum;  it  covers 
the  bladder  only  posteriorly. 

The  muscular  coat  consists  of  three  layers  of  non-striated 
muscular  fibres — namely,  an  outer  longitudinal,  a  middle 
circular,  and  an  internal  longitudinal  layer.  The  circular 
fibres  form  around  the  neck  of  the  bladder  a  thick  mus- 
cular ring — the  sphincter  vesicce. 

The  submucous  coat  consists  of  areolar  tissue  and  serves 
to  support  vessels,  etc. 

The  mucous  coat  is  lined  with  transitional  epithe- 
lium. 

The  bladder  is  supplied  with  blood-vessels  and  nerves  ; 
the  latter  are  derived  from   the   pelvic   plexus,  which   is 


MICTURITION  275 

formed  by  fibres  from  the  sympathetic  and  from  the  third, 
fourth,  and  fifth  sacral  nerves. 

The  factors  of  the  passing  of  the  urine  from  the  kidneys 
through  the  ureters  into  the  bladder  are  :  1.  The  force  of 
the  urine  constantly  formed  in  the  kidneys.  2.  The  peri- 
staltic contractions  of  the  muscular  fibres  of  the  ureters. 
3.  When  the  body  is  in  an  erect  position,  the  gravity  of 
the  urine. 

The  urine  is  eliminated  from  the  bladder  through  the 
urethra.  This  is  a  membranous  canal  which  is  lined  with 
mucous  membrane  continuous  with  that  lining  the  whole 
genito-urinary  tract. 

The  urethra  extends  from  the  neck  of  the  bladder  to  the 
meatus  urinarius,  w^hich  is  the  outer  opening  of  the  ure- 
thra. In  the  male  the  urethra  pierces  the  penis  ;  in  the 
female  it  passes  through  the  anterior  wall  of  the  vagina 
beneath  the  symphysis  pubis. 

The  Act  of  Micturition. 

The  act  of  the  evacuation  of  the  urine  which  has  col 
lected  in  the  bladder  is  called  micturition.  This  is  a  ner- 
vous reflex  act,  w^hich  to  some  extent  is  under  the  control 
of  the  will. 

The  nerves  which  regulate  the  mechanism  of  the  act  of 
micturition  are  : 

1.  A  special  nerve-centre  which  is  located  in  the  lumbar 
region  of  the  spinal  cord. 

2.  The  motor  nerve-fibres  to  the  involuntary  muscular 
fibres  of  the  walls  of  the  bladder.  These  nerve-fibres  pass 
from  the  spinal  cord  to  the  anterior  roots  of  the  third  and 
fourth  sacral  nerves. 

3.  The  motor  nerve-fibres  to  the  sphincter  urethrse. 
These  also  pass  from  the  cord  with  the  anterior  roots  of  the 
third  and  fourth  sacral  nerves. 

4.  Nerve-fibres  conducting  a  voluntary  motor  impulse  to 
the  motor  fibres  of  the  sphincter  urethras  pass  from  the 


276     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

cerebrum  through  the  spinal  cord  to  the  motor  fibres  of  the 
sphincter  urethrae  ;  the  exact  course  of  tliese  fibres  in  the 
cord  is  not  known. 

5,  Inhibitory  nerve-fibres,  which  conduct  inhibitory  im-  . 
pulses  for  the  reflex  contraction  of  the  sphincter  urethras, 
pass  from  the  brain  to  the  centre  of  micturition. 

6.  The  sensory  fibres  of  the  bladder  and  of  the  urethra 
pass  to  the  cord  in  the  posterior  roots  of  the  third,  fourth, 
and  fifth  sacral  nerves,  and  pass  up  to  the  brain,  conveying 
stimuli  which  produce  the  sensation  of  a  filled  bladder  and 
the  desire  to  mict\irate. 

The  mechanism  of  the  reflex  act  of  micturition  is  as  fol- 
lows :  The  pressure  of  the  urine  filling  the  bladder  is  a 
stimulus  which  is  conveyed  by  the  sensory  fibres  of  the 
bladder  to  the  brain,  producing  the  sensation  of  a  filled 
bladder,  and  at  the  same  time  producing  reflex  contraction 
of  the  involuntary  muscular  fibres  of  the  walls  of  the  blad- 
der. The  increased  pressure  of  the  contracting  walls  of  the 
bladder  upon  the  urine  forces  the  latter  against  the  inner 
opening  of  the  urethra  ;  the  irritation  thus  produced  causes 
a  reflex  contraction  of  the  sphincter  urethra9.  The  con- 
tinual increase  of  the  pressure  upon  the  urine  forces  drops 
of  the  same  into  the  urethra, ;  this  irritation  conveys  a 
stimulus  to  the  brain  through  the  sensory  nerves  of  the 
urethra  ;  the  result  is  that  an  impulse  inhibiting  the  reflex 
contraction  of  the  sphincter  urethrte  passes  from  the  brain, 
through  the  inhibitory  fibres,  to  the  centre  of  micturition. 

Voluntary  micturition  is  effected  by  a  voluntary  relaxa- 
tion of  the  sphincter  urethr?e  and  a  contraction  of  the  ab- 
dominal muscles  exerting  a  pressure  upon  the  bladder, 
forcing  its  contents  into  the  urethra. 

Section,  injury,  or  disease  of  the  spinal  cord  above  the 
third  sacral  nerves  causes  retention  of  urine,  because  the 
fibres  are  severed  which  conduct  inhibitory  impulses  for 
the  reflex  contraction  of  the  sphincter  urethrae.  This  mus- 
cle is  therefore  in  a  constant  state  of  contraction,  and  urine 


THE   SWEAT-GLAND.S.  277 

is  only  eliminated  by  drops  when  the  force  exerted  upon  the 
urine  filling  and  extending  the  bladder  becomes  so  strong 
that  drops  of  urine  are  forced  into  the  urethra.  Section 
of  the  cord  above  the  exit  of  the  third  sacral  nerve  also 
makes  voluntary  micturition  impossible. 

Section  of  the  anterior  roots  of  the  third  and  fourth 
sacral  nerves,  which  contain  the  motor  fibres  for  the 
sphincter  urethrse,  produces  incontinence  of  urine.  This  is 
also  produced  by  section  of  the  posterior  roots  of  these 
nerves,  for  they  contain  the  sensory  fibres  which  convey 
to  the  centre  the  stimulus  for  the  reflex  contraction  of  the 
sphincter  urethrse.  Certain  psychical  events,  such  as  fear, 
fright,  shock,  etc.,  often  cause  an  involuntary  reflex  mic- 
turition. In  infants  the  reflex  contraction  of  the  sphincter 
urethrae  is  not  so  strong  as  in  the  adult,  hence  the  invol- 
untary micturition  of  infants  whenever  the  bladder  be- 
comes filled. 

2.  TJie  Sweat-Glands  and  their  Excretion.     The  Structure 
of  the  Siveat- Glands. 

The  sweat-glands  of  the  skin  are  tubular  glands  which 
begin  as  a  coil  in  the  subcutaneous  tissue  of  the  skin; 
their  duct  is  spiral,  pierces  the  corium  and  epidermis,  and 
opens  upon  the  free  surface. 

The  glands  consist  of  a  delicate  fibrous  membrane,  the 
interior  of  which  is  lined  by  a  single  layer  of  epithelial  nu- 
cleated cells,  which  in  the  smaller  sweat  glands  have  a  flat- 
tened cubical,  and  in  the  larger  glands  a  columnar,  form. 
The  basement  membrane  of  the  larger  sweat  glands  also 
contains  plain  muscular  fibres.  The  total  number  of  sw^eat- 
glands  in  the  human  adult  is  from  2,000,000  to  2,500,000; 
they  are  most  abundant  in  the  palms  of  the  hands,  the 
soles  of  the  feet,  in  the  axillae,  and  in  the  groins. 

The  secretion  of  the  sweat  or  .sudoriferous  glands  is  an 
excretion,  because  it  contains  excrementitious  substances, 
although  only  in  minute  quantities. 


278     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Sweat  is  a  clear,  colorless  liquid  which  has  a  saline  taste 
and  generally  an  acid  reaction.  Its  chemical  composition 
is  as  follows: 

Water,  995  parts. 

Solids,       5     " 
The  solids  are: 

Organic  acids. 

Fat. 

Cholesterin. 

Urea  and  other  extractives,  about  1:1000. 

Ej^ithelial  cells. 

Inorganic  salts. 
The  excretion  of  sweat  is  regulated  by  nerve  influence. 
It  has  been  demonstrated  that  in  the  brain  and  spinal  cord 
there  are  located  special  sweat-centres.  It  is  very  likely 
that  the  activity  of  the  sweat-glands  is  due  to  special  secre- 
tory fibres;  to  a  great  extent,  however,  the  activity  of 
these  glands  is  influenced  by  vasomotor  nerves.  The  drugs 
which  increase  the  excretion  of  the  sweat — namely,  the 
diaphoretics,  ^.e.,  pilocarpine — and  the  drugs  which  de- 
crease the  excretion  of  the  sweat,  as,  for  instance,  atropine, 
act  by  their  influence  on  the  vasomotor  nervous  system. 

The  expression  "'sensible  perspiration  "  is  used  when  the 
sweat  collects  in  drops  upon  the  skin,  whereas  the  expres- 
sion "insensible  perspiration"  is  used  when  the  sweat  eva- 
porates from  the  skin  as  soon  as  it  is  excreted.  The  quan- 
tity of  water  which  is  thus  eliminated  from  the  body  in 
twenty-four  hours  by  a  healthy  adult  under  ordinary  cir- 
cumstances is  about  2  to  2|^  pounds. 


QUESTIONS   AND   EXERCISES. 

Subject. — The  Excretions. 
Lectures  XXVIII-XXIX. 

578.  Name    the    principal    excrementitious    substances 
formed  in  the  animal  body. 


QUESTIONS   AND   EXERCISES.  279 

■    579.  Name  the  princiyjal  excretory  organs  of  the  human 
body. 

580.  Distinguish  between  excretion  and  secretion. 

581.  Describe  the  microscopical  appearance  of  a  human 
kidney. 

582.  Name  the  various  portions  of  a  uriniferous  tubule, 
and  give  their  respective  diameters. 

583.  Describe  the  course  of  a  uriniferous  tubule  through 
the  substance  of  the  kidney. 

584..  Describe  the  epithelial  lining  of  the  various  portions 
of  a  uriniferous  tubule. 

585.  Descrit)e  the  course  of  the  renal  artery  through  the 
kidney,  and  point  out  any  peculiarities  in  the  vascular  sys- 
tem of  a  kidney. 

586.  Trace  the  renal  vein  through  the  kidney. 

587.  Describe  a  Malpighian  body. 

588.  What  is  the  color,  reaction,  and  specific  graidty  of 
normal  human  urine  \ 

589.  What  are  the  coloring  substances  of  the  urine  ? 

590.  Upon  what  does  the  reaction  of  the  urine  depend  ? 

591.  Give  the  variations  within  the  limit  of  health  in  the 
specific  gravity  of  urine. 

592.  Give  the  chemical  composition  of  normal  human 
urine. 

593.  Describe  urea,  its  occurrence,  variations  in  the  quan- 
tity excreted,  and  recognition  in  the  voided  urine. 

594.  What  is  the  quantity  of  urea  excreted  by  a  healthy 
adult  with  the  urine  in  twenty-four  hours  ? 

595.  Where  is  the  urea  formed  in  the  animal  body  ? 

596.  What  is  the  mechanism  of  urinary  excretion  ? 

597.  Discuss  the  nerve  influence  on  the  excretory  func- 
tion of  the  kidneys. 

598.  Describe  the  structure  of  the  ureters. 

599.  Describe  the  structure  of  the  urinary  bladder. 

600.  Describe  the  mechanism  of  micturition. 

601.  Give  the  nervous  mechanism  of  the  act  of  micturition . 


280     LECTURES   ON   HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

602.  What  is  the  average  quantity  of  urine  voided  irt 
twenty-four  hours  by  a  healthy  human  adult  ? 

603.  Mention  the  conditions  (a)  which  increase,  (b)  those 
which  decrease  this  quantity. 

604.  Describe  the  sudoriferous  glands. 

605.  What  is  the  composition  of  sweat  ? 

606.  Through  what  organs  is  the  expenditure  of  waste 
of  the  body  ? 

607.  Where  is  the  urine  formed,  and  where  its  ingre- 
dients ? 

608.  Describe  the  physiological  action  of  the  kidneys. 

609.  What  changes  take  place  in  the  blood  as  it  passes 
through  the  kidneys  ? 

610.  What  relation  does  the  nervous  system  bear  to  the 
excretion  of  perspiration  ? 

611.  What  is  the  function  of  the  sudoriferous  glands  ? 

612.  Name  the  excretory  glands  of  the  body  and  the 
function  of  each. 

613.  Explain  three  ways  by  which  waste  matter  is  ex- 
creted from  the  system. 

614.  Name  the  solids  of  the  urine,  and  state  the  approxi- 
mate amount  of  each  voided  daily  by  an  adult. 

615.  Name  and  describe  an  excreting  gland. 


LEOTUEE  XXX, 

THE   SECRETIONS. 

The  secretions  are  fluids  which  are  secreted  from  the 
blood  and  are  intended  to  serve  or  aid  physiological  pro- 
cesses. 

The  secretions  of  the  human  organism  are: 

1.  The  digestive  juices. 

2.  The  secretion  of  the  mucous,  serous,  and  synovial 
membranes. 

3.  The  milk. 

4.  The  secretion  of  the  seminal  glands. 

5.  The  secretion  of  the  lachrymal  glands. 

(d.  The  secretions  of  the  sebaceous,  Meibomian,  and  ceru- 
minous  glands  of  the  skin. 

Most  of  these  secretions  I  have  already  described,  to- 
gether with  their  uses  and  physiological  function. 

Milk  is  the  secretion  of  the  mammary  glands.  These  are 
two  lobulated  glands  situated  beneath  the  skin  in  the 
mammary  region  of  the  chest  of  the  female.  The  gland 
consists  of  lobes,  which  again  are  made  up  of  lobules,  the 
ductules,  and  larger  ducts  of  these  unite  to  form  the  lacti- 
ferous ducts,  15  to  20  in  number,  which  terminate  in  minute 
openings  in  the  nipple. 

The  structures  composing  the  gland  are  held  together 
by  areolar  and  by  adipose  tissue ;  the  external  surface  of 
the  gland  is  covered  with  skin.  The  secreting  portions  of 
the  lobules  are  lined  with  polyhedral  cells.  The  period 
when  the  glands  secrete  is  termed  the  period  of  lactation. 
This  begins  at  the  end  of  pregnancy,  shortly  before  which 
the    gland    undergoes    an  evolution ;   it  becomes  larger. 


■282      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

harder,  the  nipple  becomes^more  prominent,  and  the  pigmen- 
tation of  the  skin  surrounding  the  nipple  becomes  darker. 
At  the  same  time  changes  take  place  in  the  epithelial  cells 
lining  the  acini  of  the  gland.  At  the  termination  of  the 
period  of  lactation  the  gland  undergoes  changes  which  re- 
sult in  its  return  to  the  normal  condition  :  these  changes 
are  known  as  the  involution  of  the  gland. 

The  formation  of  milk  in  the  glands  during  the  period 
of  lactation  is  produced  by  a  fatty  metamorphosis  of  the 
epithelial  lining  of  the  glands. 

The  human  milk  is  an  emulsion  of  minute  fat  globules 
in  a  solution  of  water,  casein,  serum-albumin,  milk- sugar, 
and  inorganic  salts  ;  it  has  an  alkaline  reaction  and  a 
specific  gravity  of  1030. 

The  exact  composition  of  human  milk  and  its  value  as 
an  infant  food  I  have  already  described  in  a  former  lec- 
ture. The  use  and  function  of  human  milk  is  to  nour- 
ish the  newborn  infant  :  it  is,  therefore,  a  true  secre 
tion. 

The  secretion  of  the  seminal  glands  serves  reproductive 
functions.  T  will  describe  these,  therefore,  in  connection 
with  that  subject. 

The  secretion  of  the  lachrymal  glands  serves  to  moisten 
the  conjunctivae. 

The  secretions  of  the  sebaceous,  Meibomian,  and  the  ceru- 
minous  glands  of  the  skin  serve  to  keep  the  skin  pliable, 
to  prevent  an  undue  escape  of  water  from  the  surface,  and 
to  protect  it  from  the  macerating  effect  of  water. 

The  secretions  of  these  glands  must,  therefore,  be  de- 
scribed as  a  secretion;  they  are,  however,  considered  by 
some  as  excretions,  because,  as  a  rule,  they  contain  small 
amounts  of  excrementitious  substances. 

The  apparatus  for  the  process  of  secretion  consists  essen- 
tially of  the  following  stinictures  :  1.  Epithelial  cells.  2.  A 
basement  membrane  supporting  these.  3.  Blood-vessels. 
4.  Nerves. 


THE   SECRETIONS.  283 

The  secretory  organs  are :  1.  The  membranes.  2.  The 
glands. 

1.  The  membranes  are  the  serous,  synovial,  and  mucous. 
They  consist  of  a  basement  membrane  and,  superimposed 
upon  this,  one  or  more  layers  of  epithelial  cells.  The  secre- 
tions of  the  membranes — viz.,  that  of  the  serous  mem- 
branes, the  serous  fluid ;  that  of  the  synovial  membranes, 
the  synovia ;  and  that  of  the  mucous  membranes,  the 
mucus — serve  to  moisten  and  lubricate  these  surfaces. 

2.  The  secreting  glands  also  consist  of  a  basement  mem- 
brane, an  epithehal  lining,  and  a  blood  and  nerve  supply. 

According  to  variations  in  their  form  and  minute  struc- 
ture, the  secreting  glands  are  divided  into:  1.  Simple  tubu- 
lar, consisting  of  a  simple  tubular  depression  or  involution. 
The  mucous  follicles  in  the  mouth,  the  crypts  of  Lieber- 
kiihn,  are  glands  of  this  type. 

2.  Compound  tubular  :  In  these  the  tubules  divide  and 
subdivide.  The  glands  of  the  stomach  may  be  classed  in 
this  variety. 

3.  Racemose  or  acinous  glands,  in  which  the  secreting 
portion  consists  of  a  roundish  expansion  or  lobules,  giving 
to  the  gland  the  appearance  of  a  bunch  of  grapes.  The 
sahvary  glands,  the  pancreas,  and  the  sebaceous  glands  of 
the  skin  are  of  this  variety.  The  racemose  glands  are  by 
some  authorities  further  subdivided  into  simple  and  com- 
pound racemose  glands. 

The  process  of  secretion  is  effected  by  physical  and  chemi- 
cal processes. 

The  physical  processes  are  (o)  filtration  and  (6)  diffusion. 

The  chemical  processes  consist  in  the  formation  of  cer- 
tain ingredients  of  the  secretion  which  do  not  pre-exist  as 
such  in  the  blood,  but  are  the  product  of  chemical  pro- 
cesses taking  place  in  the  cells. 

The  process  of  secretion  of  an  organ  may  be  continuous 
•or  it  may  be  interruptted.  The  process  is  infl.uenced  by  : 
1.  The  blood  supply  to  the  gland.    2,  The  nerve  supply. 


284     LECTURES   ON   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

The  character  of  a  secretion  depends  to  a  certain  extent- 
upon  a  physiological  property  of  the  epithelium  of  the- 
secreting  organ.  This  special  property  of  these  cells  con- 
sists in  a  special  affinity  for  certain  materials  of  the  blood, 
and  in  a  peculiar  elaboration  of  certain  materials  within 
these  cells. 

THE   SKIN  AND   ITS   FUNCTIONS. 

The.  structure  of  the  Skin. 

The  skin  is  a  membrane  which  covers  the  exterior  of  the^ 
body.  It  is  from  2  to  3  millimetres  thick  and  rests  upon 
a  sabcutaneous  cellular  tissue.  The  latter  is  composed  of 
an  areolar  network  and  contains  more  or  less  adipose 
tissue  ;  it  serves  to  support  the  blood-vessels,  nerves,  and 
other  structures  of  the  skin. 

The  skin  i^roper  consists  of  the  coriuin  or  cutis,  and  the 
epidermis  or  cuticle. 

The  corium,  or  cutis  vera,  rests  upon  the  subcutaneous 
and  adipose  tissue.  It  is  composed  of  a  reticulum  of  elas- 
tic and  white  fibres,  which  consists  of  many  layers  ;  these, 
passing  in  all  directions,  form  a  dense  and  elastic  struc- 
ture. In  the  deeper  layers  the  meshes  of  the  reticulum 
are  larger  and  contain  fat ;  the  upper  layers  are  very  dense 
and  interwoven  with  plain  muscular  fibres.  From  the  sur- 
face of  the  cutis  vera  are  projected  numerous  cone-like 
elevations  called  the  papillce ;  they  have  either  a  single  or 
branched  free  extremity.  These  papilla?  are  most  impor- 
tant, for  they  are  organs  of  the  special  sense  of  touch; 
they  contain  capillary  blood-vessels  and  the  terminals  of 
sensory  nerves — viz.,  the  tactile  corpuscles. 

The  papilla;  are  most  abundant  in  the  skin  of  the  palms 
of  the  hands  and  the  soles  of  the  feet,  and  it  is  for  this 
reason  that  in  these  parts  the  sense  of  touch  is  more  acute 
than  in  other  portions  of  the  body.  I  will  describe  the  tac- 
tile corpuscles  with  the  subject  of  the  special  sense  of 
touch. 


THE   SKIN   AND   ITS   FUNCTIONS.  285 

The  epidermis,  or  cuticle,  consists  of  numerous  layers  of 
cells  which  are  superimposed  upon  the  cutis  vera,  and 
which  are  held  together  by  an  intercellular  cementing  sub- 
stance. The  cells  of  the  epidermis  are  arranged  in  four 
distinct  strata,  each  consisting  of  cells  of  varying  shapes. 
These  four  strata  are  : 

1.  The  stratum  corneiim,  which  consists  of  numerous 
layers  of  squamous,  horny  cells.  The  varying  thickness  of 
these  layers  produces  the  variations  in  the  thickness  of  the 
skin  in  the  different  parts  of  the  body,  as  the  other  struc- 
tures of  the  skin  have  a  more  or  less  uniform  thickness. 

2.  The  stratum  lucidum  is  situated  beneath  the  former. 
It  consists  of  layers  of  flattened  cells  which  have  a  clear, 
homogeneous  protoplasm,  and  sometimes  have  nuclei. 

3.  The  stratum  gramdosum  consists  of  a  layer  of  flat- 
tened cells  which  have  a  granular  protoplasm  and  a 
distinct  nucleus. 

4.  The  stratum  Malpighii,  or  rete  mucosum,  consists  of 
many  layers  of  various  shaped  cells.  The  deepest  layer 
consists  of  cells  which  are  nucleated  and  have  a  columnar 
form.  These  cells  cover  in  a  uniform  layer  the  cutis  vera 
and  its  papillae.  The  layers  external  to  this  layer  of  colum- 
nar cells  consist  of  many-sided  cubical  cells.  The  middle 
layers  of  the  rete  Malpighii  consist  of  branched  cells  which 
are  connected  by  their  processes  and  are  called  prickle 
cells.  The  outer  layers  of  the  rete  Malpighii  consist  of 
more  flattened  cells. 

The  deeper  layers  of  the  stratum  or  rete  Malpighii  con- 
tain the  pigment  to  which  the  coloration  of  the  skin  is 
due. 

The  epidermis  serves  to  protect  the  cutis  vera.  The 
touching  of  clothes,  friction,  handling,  and  other  mechani- 
cal injuries  to  which  the  surface  of  the  body  is  subjected, 
cause  a  constant  wearing-off  of  the  outer  layers  of  the 
stratum  corneum  of  the  epidermis.  This  is  replaced  by 
cells  from  the  deeper  layers,  so  that  the  epidermis  con- 
stantly maintains  its  thickness.     This  new  formation  of 


286     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

cells  in  the  deeper  layers  of  the  epidermis  takes  place  in 
such  a  manner  that  the  columnar  cells  of  the  rete  Mal- 
pighii  divide  into  a  lower  portion  which  retains  the  colum- 
nar shape,  and  an  upper  portion  which  assumes  the  more 
polyhedral  form  of  the  cells  of  the  middle  layers  of  the 
epidermis.  By  the  constant  repetition  of  this  process  the 
new-formed  cells  are  pushed  toward  the  outer  layers  of 
the  epidermis,  and  in  the  stratum  corneum  they  become 
more  and  more  flattened  and  scaly. 

The  Glands  of  the  Skm. 

The  skin  is  provided  with  two  sets  of  glands — namely, 
the  sudoriferous  or  sweat-glands  and  the  sebaceous  glands. 

The  sudoriferous  glands  and'  their  secretion,  the  sweat, 
I  have  already  described  in  my  last  lecture  when  speaking 
of  the  excretory  organs  and  of  the  excretions. 

The  sebaceous  glands  are  small,  compound  racemose 
glands;  they  are  most  abundant  in  the  parts  of  the  body 
which  are  supplied  with  hair;  they  are  absent  in  the  skin 
of  the  palmar  surface  of  the  hand  and  plantar  surface  of 
the  foot. 

The  sebaceous  glands  consist  of  a  lobulated,  secreting 
portion  which  is  lined  with  jjolyhedral,  flattened,  nucle- 
ated cells,  and  a  duct  which  opens  either  direct  upon  the 
skin  or  into  a  hair-follicle  at  its  side.  The  interior  of  these 
glands  is  filled  with  a  whitish,  soft,  fatty  matter  called  the 
sebum,  formed  as  the  product  of  the  proliferation,  fatty 
degeneration,  and  final  breaking-down  of  the  cells  lining 
the  glands. 

The  chemical  composition  of  the  sebum  is  as  follows: 
fats,  as  olein  and  palmitin;  cholesterin;  albuminous  mat- 
ter; extractives;  organic  acids — butyric,  oaproic,  etc.;aro- 
matics;  inorganic  salts,  principally  insoluble  phosphates. 

Examined  under  the  microscope  the  sebum  contains  fat 
granules,  cholesterin  crystals,  epithelial  cells,  and  a  pecu- 
liar micro-organism,  the  demodex  folliculorum. 


THE    SKIN   AND    ITS   FUNCTIONS.  287 

The  sebum  is  an  oily  liquid;  sometimes  it  becomes  semi- 
solid in  the  gland,  forming  the  so-called  comedones. 

The  secretion  of  the  sebaceous  glands  serves  to  keep  the 
skin  and  hair  soft  and  pliable,  to  prevent  an  undue  escape 
of  moisture,  and  to  protect  the  skin  from  the  effects  of 
long-continued  exposure  to  moisture. 

The  Meibomian  glands  of  the  eyelids,  and  the  cerumin- 
ous  glands  of  the  skin  covering  the  interior  of  the  external 
ear,  are  tubular  glands  resembling  in  their  structure  the 
sudoriferous  glands;  their  secretion,  how^ever,  in  its  com- 
position resembles  to  a  greater  extent  the  sebum  and 
serves  the  same  purpose. 

The  Hair. 

The  skin  is  covered  in  almost  all  locations  with  hair;  in 
some  parts  it  is  thick  and  strong,  in  others  very  thin  and 
delicate  and  called  lanugo.  A  hair  is  the  result  of  a 
peculiar  development  of  the  epidermis.  It  consists  of  an 
external  layer  of  flat,  scaly  cells  which  are  arranged  like 
tiles,  with  the  free  edge  upward;  this  layer  is  called  the 
cuticle  of  the  hair.  Beneath  this  there  is  a  layer  of  thick, 
elongated  horny  cells.  In  the  centre  of  a  hair  there  is 
sometimes  a  space  which  is  filled  with  smaller  cells,  pig- 
ment granules,  and  fat;  this  is  called  the  medulla  of  the 
hair. 

The  lower  portion,  or  root,  of  each  hair  is  contained  in  a 
tubular  depression  from  the  skin;  this  is  called  the  hair- 
follicle.  It  descends  into  the  subcutaneous  cellular  and 
adipose  tissue,  where  it  terminates  in  a  bulbous  expansion. 
The  follicle  consists  of  a  delicate  basement  membrane 
which  is  surrounded  by  blood-vessels;  its  interior  is  lined 
with  squamous  cells  continuous  with  those  covering  the 
exterior  of  the  epidermis.  From  the  fundus  of  the  hair- 
follicles  a, papilla  projects  into  the  cavity  of  the  same;  this 
papilla  is  composed  of  the  structures  of  the  cutis  and 
is  covered  on  its  surface  by  epidermal  cells.     The  hair  is 


288     LECTURES   ON   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

formed  by  a  peculiar  development  and  growing  upward  of 
the  epidermal  cells  covering  the  hair-pa])illa. 

Into  the  hair-follicle  at  its  side  opens  generally  one, 
sometimes  two,  sebaceous  glands. 

From  the  fibrous  membrane  to  the  upper  layer  of  the 
cutis  there  passes  a  layer  of  plain  muscular  fibres:  a  con- 
traction of  these  causes  the  standing-up  of  the  hair,  and, 
by  the  pressure  upon  the  sebaceous  glands,  forces  their 
contents  into  the  hair-follicle. 

The  hair-follicles  are  supphed  with  nerve-fibrilli  which 
terminate  in  the  plain  muscular  fibres  of  the  follicle. 
These  nerve-fibres  arise  in  the  spinal  cord  and  are  contained 
in  the  sympathetic  nerve-trunks ;  stimulation  of  these 
causes  the  stauding-up  of  the  hair  in  the  localities  to  which 
they  are  distributed. 

Hair  begins  to  develop  in  the  twelfth  or  thirteenth  week. 
During  the  nineteenth  to  twenty-fifth  week  the  hair  begins 
to  cover  the  skin  of  the  foetus. 

The  color  of  the  hair  is  due  to  the  development  of  pig- 
ment in  the  medulla.  The  gray  color  of  hair  in  advanced 
age  is  due  to  insufficient  development  of  pigment  and  to 
the  presence  of  air-bubbles  in  the  medulla.  These,  owing 
to  their  refractive  power,  give  to  the  gray  hair  the  silvery, 
glistening  appearance.  The  sudden  gray  discoloration  of 
hair  produced  by  psychical  events,  such  as  fright,  fear, 
etc..  is  believed  to  be  due  to  the  production  of  such  air- 
bubbles  in  the  medulla. 

Tlie  Xails. 

The  nails,  like  the  hair,  are  produced  by  a  peculiar  de- 
Telopment  of  the  epidermis.  A  nail  projects  from  a  con- 
vex groove  in  the  skin  of  the  dorsum  of  the  digit.  It 
projects  beyond  the  end  of  the  digit,  and  rests  with  its 
lower  surface  upon  the  dorsal  surface  of  the  end  of  the 
digit.  The  convex  groove  in  the  skin  of  the  dorsum  of 
the  digit  in  which  the  root  of  the  nail  is  lodged  is  termed 


THE   SKIN   AND    ITS   FUNCTIONS.  289 

the  matrix  of  the  nail.  The  flat  surface  of  the  digit,  upon 
which  the  nail  rests  with  its  under- surface,  is  called  the 
bed  of  the  nail.  The  matrix  is  formed  by  a  peculiar  ar- 
rangement of  the  cutis  vera.  It  is  covered  with  elevated 
ridges,  and  from  the  epidermal  cells  covering  them  the 
nail  develops  as  a  result  of  the  constant  multiplication  and 
pushing  forward  of  these  cells.  The  nail  consists  of  va- 
rious layers  of  epidermal  cells^  the  outer  ones  being  very 
horny. 

The  Functions  of  the  Skin. 

The  skin  possesses  several  important  functions.  These 
may  be  enumerated  as  follows  : 

1.  The  skin  is  an  excretory  organ.  I  have  already 
spoken  of  this  function  in  my  last  lecture  when  speaking 
of  the  sudoriferous  glands  and  their  secretion,  the  sweat. 
The  importance  of  the  skin  as  an  excretory  organ  is  best 
shown  in  pathological  disturbances  of  the  excretory  func- 
tions of  the  kidneys,  in  which  the  skin  often  tends  to  aid 
in  the  elimination  of  excrementitious  substances  from  the 
iDody.  For  instance,  in  urcemia  the  percentage  of  urea  in 
the  sweat  is  greatly  increased.  The  secretions  of  the  other 
glands  of  the  skin  must  also,  to  a  certain  extent,  be  con- 
sidered as  excretions.  It  has  been  observed  that  when  the 
excretory  function  of  the  skin  has  been  interfered  with, 
compensation  for  this  is  made  by  the  kidneys. 

2.  The  skin  prevents  an  undue  escape  of  heat  from  the 
surface  of  the  body,  because  the  subcutaneous  cellular  and 
adipose  tissue,  the  cutis  vera,  and  the  epidermis  are  bad 
conductors  of  heat. 

8.  The  skin  protects  the  surface  of  the  body,  ia)  The 
delicate  anatomical  structures  on  the  surface  of  the  body 
are  protected  by  the  soft  subcutaneous  tissue  and  by  the 
elastic,  tough,  leathery  skin  covering  it.  [h)  The  absorp- 
tion of  poisonous  substances  is  prevented  by  the  thick 
layers  of  the  epidermis  and  by  the  fatty  secretion  of  the 

19 


290      LECTURES    ON   HUMAN    PHYSIOLOGY   AND   HISTOLOGY. 

sebaceous  glands.  Skin  does  not  absorb  substances  from 
a  watery  solution,  but  does  so  from  solutions  which  dis- 
solve the  sebaceous  secretions — viz.,  alcohol,  ether,  and 
chloroform.  The  epidermis,  and  the  fatty  sebaceous  matter 
permeating  it,  protect  the  cutis  and  underlying  parts  from 
the  macerating  effect  of  a  long-continued  exposure  to- 
moisture. 

4.  The  skin  is  an  organ  of  respiration.  In  connection 
with  the  subject  of  respiration  I  have  already  spoken  of 
the  respiratory  activity  of  the  skin. 

5.  The  soft  adipose  and  subcutaneous  cellular  tissue  and 
the  elastic  skin  serve  to  protect  underlying  delicate  struc- 
tures, to  fill  out  depressions  and  irregularities,  and  to  cover 
rough  surfaces,  thus  giving  to  the  surface  of  the  body 
a  round  and  plastic  form. 

6.  The  skin  is  an  organ  of  touch.  This  function  the 
skin  possesses  owing  to  the  nerve  terminations — viz.,  the 
tactile  corpuscles  in  the  papillae  of  the  cutis  vera. 

From  this  description  and  enumeration  of  the  functions 
and  uses  of  the  skin  the  importance  of  this  structure  will 
be  clearly  understood.  It  has  been  demonstrated  that  ani- 
mals whose  skin  has  been  varnished  soon  die. 

Loss  of  a  large  surface  of  skin  by  burns  or  other  injuries 
is  often  followed  by  serious  disturbances,  and  necessitates 
replacement  of  skin  by  plastic  operations  or  skin  grafting. 


QUESTIONS   AND   EXERCISES. 

Subject. — The  Secretions.     The  Skin  and  its  Functions. 
Lecture  XXX. 

616.  What  do  you  understand  by  secretion? 

617.  Name  the  secretions  of  the  body  and  give  the  func- 
tions of  each. 

618.  Describe  the  mammary  glands. 

619.  Give  the  composition  and  uses  of  human  milk. 


QUESTIONS   AND   EXERCISES.  291 

620.  Describe  the  structure  of  the  skin. 

621.  Name  the  glands  of  the  skin. 

622.  What  are  the  functions  of  the  skin? 

623.  Describe  the  sebaceous  glands. 

624.  What  are  the   composition    and    function   of    the 
secretion  of  the  sebaceous  glands? 

625.  What  are  (a)  the  Meibomian  glands?  (5)  the  ceru- 
minous  glands? 

626.  What  is  the  function  of  the  sudoriferous  glands? 

627.  Describe  the  structure  of  a  hair. 

628.  Describe  the  structure  of  a  nail. 

629.  Name  and  describe  the  various  layers  of  epidermis. 

630.  Name  the  essential  structures  of  a  secreting  appa- 
ratus. 

631.  Name  the  secretory  organs  of  the  human  body. 

632.  Name  the  membranes  and  their  secretions. 

633.  Name  and  describe  the  varieties  of  secreting  glands. 
Give  examples  of  each. 

634.  Name  the  conditions  influencing  secretion. 

635.  By  what  processes  is  secretion  effected? 

636.  Upon  what  does  the  nature  of  a  secretion  depend? 

637.  How  is  secretion  produced  when  food  enters  the 
mouth? 

638.  Define  secretion. 


LECTUEE  XXXI. 

THE  FORCES  OF  THE  ANIMAL  ORGANISM. 

1.  Animal  Heat.     2.  Animal  Motions. 

The  metabolism  of  the  animal  organism  results  in  a 
production  of  living  forces. 

Living  or  kinetic  force  is  the  force  which  manifests  itself 
as  heat,  light,  electricity,  and  mechanical  work.  The  im- 
perceptible force  which  exists  in  all  matter  is  termed  po- 
tential  force. 

The  physical  laws  relating  to  the  forces  in  nature  assert 
that  there  is  no  spontaneous  generation  or  destruction  of 
force,  but  that  a  new  form  of  force  results  from  a  change 
of  some  other  form. 

In  the  animal  organism  the  potential  forces  which  are 
stored  in  the  nutritive  materials  taken  are  transformed 
into  living  forces.  In  the  human  organism  two  forms  of 
living  force  are  observed — namely,  animal  heat  and  ani- 
mal motions. 

Formerly  the  manifestations  of  animal  heat  and  animal 
motions,  and  physiological  processes  such  as  growth,  devel- 
opment, and  metabolism  of  the  tissues,  were  considered  as 
manifestations  of  a  force  peculiar  to  living  organisms, 
which  was  called  the  vital  force.  At  the  present  time  this 
is  not  considered  a  satisfactory  explanation  by  most  scien- 
tists, but  it  is  believed  that  also  these  more  complicated 
physiological  phenomena  are  the  result  of  physical  and 
chemical  processes    of  a  complicated    nature    not    fully 

understood. 

1.  Animal  Heat. 

The  heat  which  is  constantly  generated  in  the  animal 


ANIMAL    HEAT.  293 

body  is  called  animal  heat,  which  must  be  considered  as 
a  rapid  vibration  of  the  atoms  composing  the  matter  of 
the  animal  body,  caused  by  the  constant  molecular  changes 
taking  place  in  the  body  ingredients.  The  potential  force 
contained  in  these  may  be  considered  as  latent  heat  which 
is  transformed  into  a  living  force — namely,  measurable 
heat. 

The  science  which  treats  of  the  temperature  of  bodies  is 
called  thermometry.  The  instruments  used  to  determine 
the  degree  of  heat  of  bodies  are  the  thermometer  and  the 
thermo-electrical  apparatus. 

It  has  been  observed  that  many  animals  maintain  a  body 
temperature  independent  of  any  thermal  changes  in  the 
surrounding  atmosphere;  such  animals  are  called  homoio- 
thermal  animals.  Their  body  temperature  is  generally 
higher  than  that  of  the  surrounding  atmosphere;  they  are 
consequiently  warm  to  the  touch,  and  are  called  warm- 
blooded  animals.  Other  animals,  again,  change  their  tem- 
perature with  that  of  the  medium  in  which  they  live;  they 
are  called  p)oikilothermal  animals;  they  are  generally  cold 
to  the  touch,  and  are  called  cold-blooded  animals.  The 
mammalia,  birds,  and  man  are  homoiothermal;  the  fishes 
and  reptiles  are  poikilothermal  animals. 

The  average  temperature  of  the  human  body  in  health  is 
9S.(3°  F.  =  37'  C. 

The  temperature  of  the  human  body  varies  in  different 
parts.  As  a  rule  it  may  be  said  that  it  is  lower  in  the  parts 
most  exposed,  which  are  least  active,  and  in  which  the  least 
chemical  processes  take  place;  and  that,  on  the  other  hand, 
it  is  highest  in  the  parts  least  exposed,  which  are  most  ac- 
tive, and  in  which  the  greatest  chemical  changes  take  place, 
as  in  the  internal  organs,  muscles,  and  glands.  Thermo- 
metrical  observations  have  shown  that  venous  blood  is  a 
little  warmer  than  arterial;  that  the  blood  in  the  right  side 
of  the  heart  is  a  httle  warmer  than  that  of  the  left  side; 
and  that  the  blood  in  the  hepatic  veins  and  in  the  liver  is 


294     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

almost  1°  C.  warmer  than  that  in  the  aorta.  Furthermore, 
it  has  been  observed  that  the  temperature  of  the  muscles, 
organs,  and  glands  is  higher  during  their  activity  than 
during  rest.  All  these  variations  are  but  slight,  and  it  may 
be  stated  that  the  temperature  in  the  various  parts  of  the 
human  body  varies  from  98.6°  F.  to  100.4°  F.  =  37°  to  38°  C. 

The  instrument  most  used  by  the  clinician  to  ascertain 
the  body  temperature  of  individuals  is  the  clinical  ther- 
mometer. 

Sandorius,  in  1626,  made  the  first  thermometrical  obser- 
vations on  the  human  body.  To  day  the  clinical  thermo- 
meter is  the  principal  instrument  in  the  armamentarium 
of  the  physician.  In  this  country  thermometers  with  the 
Fahrenheit  scale  are  employed,  while  in  European  countries 
the  Celsius,  or  centigrade,  scale  is  generally  used. 

To  obtain  the  body  temperature  the  thermometer  is 
placed  in  the  mouth  under  the  tongue,  in  the  vagina,  or  in 
the  rectum;  the  latter  location  is  preferaljle. 

Careful  observations  have  demonstrated  the  fact  that  the 
temperature  of  the  human  body  in  health  shows  diurnal 
variations.  During  the  day  it  continually  rises,  reaching 
its  maximum  between  6  and  S  p.m.,  and  during  the  night  the 
temperature  continually  decreases,  reaching  its  minimum 
at  3  to  6  A.M.  The  temperature  is  increased  by  muscular 
exercise  and  after  taking  food;  it  is  decreased  by  fasting 
and  rest.  Climatic  conditions  to  some  extent  influence  the 
body  temperature;  it  is  slightly  increased  during  the  sum- 
mer and  decreased  in  cold  weather.  Sex  and  race  appa- 
rently do  not  influence  the  body  temperature. 

In  children  and  infants  the  temperature  is  generally 
lower  than  in  middle-aged  persons:  in  old  age  it  is  again 
lower.  All  conditions  which  influence  the  metaboUsm  of 
the  tissues — pathological  conditions,  many  drugs,  surgical 
operations,  etc. — often  influence  the  body  temperature,  and 
it  is  for  this  reason  that  the  clinician  should  be  perfectly 
famihar  with  the  subject  of  thermometry. 


AXIMAL   HEAT.  595 

The  principal  source  of  animal  heat  is  the  oxidation  or 
combustion  of  the  nutritive  materials  in  the  body. 

The  oxygen  required  for  the  combustion  is  taken  through 
the  lungs.  The  main  quantity  of  the  animal  heat  is  pro- 
duced by  the  combustion  of  the  carbon  of  the  organic  nu- 
tritive materials  with  the  production  of  carbon  dioxide. 
About  25  per  cent  of  the  animal  heat  is  produced  by  the 
combustion  or  oxidation  of  the  hydrogen  of  the  nutritive 
materials  Tvith  the  production  of  water.  A  small  quantity 
of  heat  is  produced  in  the  body  by  other  chemical  pro- 
cesses: friction,  motion,  etc.,  also  tend  to  produce  heat. 

We  may  therefore  enumerate  the  sources  of  animal  heat 
as  follows: 

1.  The  combustion  of  carbon. 

2.  The  combustion  of  hydrogen. 

3.  Other  chemical  processes. 

4.  Physical  processes,  such  as  friction,  motion,  electrical 
currents  in  muscles,  glands,  etc. 

It  may  be  said,  however,  that  when  the  body  is  at  rest 
the  entire  potential  force  contained  in  the  nutritive  mate- 
rials is  transformed  into  heat.  The  products  resulting 
from  the  combustion  of  the  nutritive  materials  of  the  body 
contain  a  much  smaller  quantity  of  potential  force  than  the 
nutritive  materials.  The  production  of  animal  heat  con- 
sists, therefore,  in  a  transformation  of  materials  with  a  higli 
potential  force  into  substances  with  a  low  potential  force. 

The  quantity  of  heat  which  is  produced  by  the  oxida- 
tion or  combustion  of  the  various  substances  can  be  mea- 
sured, and  is  expressed  by  heat-units  or  gramme-ccdories. 

One  heat-unit  or  one  gramme-calorie  is  the  quantity  of 
heat  required  to  raise  the  temperature  of  one  cubic  centi- 
metre of  water  one  degree  centigrade. 

The  science  which  treats  of  the  study  and  methods  of 
ascertaining  the  quantity  of  heat  contained  in  a  body,  or 
the  quantity  of  heat  which  is  produced  by  its  combustion, 
is  termed  caJorimetrij. 


296     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  apparatus  generally  used  for  these  experiments  i& 
the  water-calorimeter. 

A  water-calorimeter  cousists  of  a  cylmdrical  box,  the 
combustion  chamber,  which  receives  the  materials  to  be 
burned.  This  is  suspended  in  a  vessel  which  contains  a 
stated  quantity  of  water  of  a  stated  temperature.  This 
vessel  is  surrounded  by  a  thick  layer  of  material  which  is  a 
poor  conductor  of  heat,  and  is  again  suspended  in  another 
vessel  with  water.  The  non-conducting  surrounding  of 
the  walls  of  the  inner  cylinder,  and  the  water  in  the  outer 
cylinder,  serve  to  prevent  an  escape  of  heat.  The  water  in 
the  inner  cylinder,  in  which  the  combustion-chamber  is 
suspended,  is  heated  by  the  heat  produced  by  the  burning 
of  materials  in  the  combustion-chamber.  The  quantity 
and  temperature  of  the  water  in  this  inner  cylinder  are 
ascertained  and  noted  before  the  beginning  of  the  process 
of  combustion  ;  during  this  the  increase  of  the  tempera- 
ture of  the  water  in  the  inner  cylinder  is  noted  by  mean& 
of  a  thermometer.  The  upper  portion  of  the  whole  ap- 
paratus is  closed  by  covers  made  of  non-conducting  mate- 
rials. Through  these  covers  four  tubes  pass  into  the  com- 
bustion-chamber. One  tube  is  provided  with  a  glass  plate 
and  a  mirror ;  this  permits  an  observation  of  the  process 
in  the  combustion-chamber. 

The  second  tul)e  passes  nearly  to  the  floor  of  the  combus- 
tion-chamber ;  this  serves  to  admit  the  air  required  for 
the  combustion.  A  third  tube  leading  into  the  combus- 
tion-chamber serves  to  introduce  gases  when  the  heat 
produced  by  their  combustion  is  to  be  ascertained.  This 
tube  is  closed  by  a  stop-cock. 

The  fourth  tube  consists  of  a  lead  coil  which  passes 
through  the  water  surrounding  the  combustion-chamber; 
it  opens  into  this  at  its  upper  portion.  This  tube  serves  to 
give  exit  to  the  ga=es  formed  in  the  combustion-chamber 
during  combustion;  these  gases,  while  passing  through 
the  many  coils  of  the  leaden  tube,  cool  by  transmitting 


ANIMAL    HEAT.  297 

their  heat  to  the  metalhc  walls  of  the  tube,  which  again 
transmit  it  to  the  water  through  which  the  tube  winds. 
Knowing  the  exact  quantity  of  water  contained  in  tha 
inner  cylinder,  and  its  exact  temperature  before  the  pro- 
cess of  combustion  begins,  and  knowing  the  cj^uantity  of 
material  burned  in  the  combustion-chamber,  it  remains 
ODly  to  ascertain  the  temperature  of  the  water  contained 
in  the  inner  cyhnder  after  the  complete  combustion  of  the 
substance  in  the  combustion-chamber,  and  it  is  then  easy 
to  calculate  the  numljer  of  heat-units  of  the  substance 
biu^ned  in  the  combustion- chamber. 

Favre.  Silverman,  and  others  have  determined  by  calori- 
metric  experiments  the  quantity  of  heat  produced  by  the 
complete  oxidation  of  carbon,  hydrogen,  and  of  the  prin- 
cipal nutritive  materials.  The  results  of  these  experi- 
ments, expressed  in  heat-units,  are  as  follows  : 

Carbon.  8,100. 

Hydrogen,  3,450. 

Albumen,  4,995. 

Fat,  9,069. 

Carbohydrates.  9.745. 
The  combustion  of  these  substances  in  the  calorimeter  is 
much  more  rapid  than  in  the  animal  body,  but  it  is  other- 
wise the  same  process. 

Fats  and  carbohydrates  are  completely  oxidized  in  the 
body.  Albuminous  substances  are  not  completely  oxi- 
dized: about  one-third  of  their  weight  is  excreted  as 
urea,  which  has  2,206  heat-units.  One-third  of  this  must 
therefore  be  subtracted  from  the  heat  produced  by  the 
complete  oxidation  of  albumen,  so  that  the  heat  produced 
by  the  combustion  of  one  gramme  of  albumen  in  the  hu- 
man body  equals  only  4,263  heat-units. 

Knowing  the  quantity  of  heat-units  produced  by  the 
combustion  of  one  gramme  of  each  of  the  food  or  nutritive 
materials,  it  is  easy  to  determine  the  total  quantity  of  heat- 
units  produced  in  the  body  by  determining  the  number  of 


298     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

grammes  of  each  of  the  nutritive  materials  taken  with  the 
food.  From  this  it  has  been  estimated  that  in  the  body  of 
a  healthy  man  taking  a  mixed  diet  of  125  grammes  of 
albumen,  80  grammes  of  fat,  and  300  grammes  of  carbo- 
hydrates, about  3,000,000  heat-units  are  produced.  This 
number,  however,  is  not  exact,  as  a  portion  of  the  food 
materials  is  always  unabsorbed,  and  it  has  been  calculated 
that  the  loss  of  heat  thus  caused  is  about  8  per  cent  of  the 
total  amount,  which,  subtracted  from  the  amount  given, 
leaves  about  2,800,000  as  the  total  number  of  heat-units 
produced  in  the  human  body  under  the  conditions  men- 
tioned. 

This  quantity  of  heat  which  is  produced  in  the  body  by 
the  combustion  of  materials  constitutes  about  75  per  cent 
of  the  total  amount  of  heat  generated  in  the  body.  The 
remaining  25  per  cent  is  produced  by  other  chemical  pro- 
cesses and  by  physical  action. 

The  temperature  of  the  animal  body  is  regulated: 

1.  By  a  constant  elimination  of  heat  from  the  body. 

2.  By  the  constant  heat  production  in  the  body. 

Both  the  production  and  elimination  of  heat  are  influ- 
enced by  various  conditions,  such  as  the  quantity  and  qua- 
lity of  food  taken,  the  external  temperature,  nerve  influ- 
ence, muscular  action,  the  blood-supply,  etc.  Experiments 
which  have  been  made  to  ascertain  the  comparative  amount 
of  heat  which  is  given  off  from  the  body  in  various  ways 
have  given  the  following  results. 

Of  the  total  quantity  of  heat  produced  in  the  body, 
80.5  per  cent  is  given  off  from  the  skin  by  radiation  and 
evaporation  ;  14.5  per  cent  is  given  off  by  evaporation 
from  the  lungs;  2.5  per  cent  is  given  off  with  the  expired 
air;  2.5  is  given  off  w^ith  the  urine  and  faeces. 

The  production  of  heat  within  the  body,  and  the  elimina- 
tion of  heat  from  the  body,  regulate  themselves  in  such  a 
manner  as  to  keep  the  temperature  of  the  body  at  a  certain 
degree. 


ANIMAL   HEAT.  299 

During  cold  weather  the  vessels  of  the  surfaces  of  the 
hody  contract,  decreasing  the  blood-supply  to  these,  and 
i}hus  decreasing  the  giving-off  of  heat  from  the  surfaces 
of  the  body.  During  warm  weather  the  reverse  condition 
takes  place:  the  vessels  dilate,  more  blood  is  supplied,  and 
consequently  more  heat  is  given  off;  the  increased  blood- 
supply  also  causes  an  increased  excretion  of  sweat,  with 
which  a  quantity  of  heat  is  eliminated.  The  same  condi- 
tions take  place  when  the  heat  production  is  increased  by 
great  muscular  activity. 

The  heat  production  within  the  body  is  to  a  certain  ex- 
tent self -regulating.  In  cold  weather  the  process  of  com- 
bustion is  more  active  than  in  summer.  This  is  shown  by 
the  fact  that  in  cold  weather  the  consumption  of  oxygen 
and  the  production  of  carbon  dioxide  are  greater  than  in 
summer.  Another  factor  in  the  regulation  of  heat  produc- 
tion is  muscular  activity;  this  is  more  active  in  cold  than 
in  warm  weather. 

It  has  been  shown  that  heat  regulation  in  the  body  is 
also  influenced  by  nerves.  Section  of  larger  nerves  is  fol- 
lowed by  an  increased  temperature  in  the  parts  supplied  by 
the  nerve.  Section  of  the  spinal  cord  is  followed  by  an 
increased  temperature  in  the  parts  below  the  point  of  sec- 
tion. Injury  to  the  brain  in  the  vicinity  of  the  pons  Varolii 
and  medulla  oblongata  is  also  followed  by  a  rise  in  the  body 
temperature.  These  observations  tend  to  show  that  the 
Tjody  temperature  is  influenced  by  nerves,  and  it  was  for- 
merly believed  that  there  were  special  caloric  nerves  and 
centres;  later  observations,  however,  have  shown  that 
these  thermal  changes  are  caused  by  a  dilatation  of  the 
blood-vessels  resulting  from  section  or  injury  or  irritation 
of  vasomotor  nerves  and  centres. 

An  increased  normal  body  temperature  is  termed  fever 
This  is  a  constant  symptom  of  many  pathological  condi- 
tions, and  is  caused  either  by  the  increase  of  the  heat  pro- 
duction in  the  body,  a  decrease  of  the  heat    elimination 


300     LECTURES   ON    HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

from  the  body,  an  increase  of  the  metabolism  of  the  tissues, 
or  a  disturbance  of  the  regulation  of  the  body  temperature. 
Fever  is  generally  accompanied  by  a  rapid  pulse,  rapid 
respiration,  and  dry  and  red  skin.  A  temperature  of  100°  to 
102°  F.  indicates  a  mild  fever;  a  higher  temperature  shows 
severe  fever.  High  fever  often  causes  death  by  its  inter- 
ference with  many  of  the  important  physiological  processes 
of  the  body.  Long-continued  febrile  conditions  are  often 
followed  by  fatty  degeneration  of  muscular  tissues. 

The  body  temperature  can  be  artificially  raised  and 
lowered.  Cold  baths  decrease  the  temperature,  and  are 
often  used  for  this  purpose  in  the  treatment  of  fevers. 

Exposure  of  the  body  to  air  having  a  very  low  tempera- 
ture interferes  with  the  heat  regulation  of  the  body. 

Persons  overcome  by  exposure  to  cold  air  are  often  found 
to  have  a  subnormal  temperature;  a  recovery  in  these  cases 
is  rare.  Exposure  of  the  body  to  hot  air  interferes  with 
the  heat  elimination  from  the  body,  and  an  increase  of  the 
body  temperature  is  the  result. 


LECTURE   XXXIL 

ANIMAL  MOTIONS. 

1.  Muscular  Motion.     2.  Ciliary  Motion.     3.  Protoplasmic 

Motion. 

I.  Muscular  Motion. 

The  muscles  are  the  active  organs  which  effect  the  mo- 
tions of  the  body  and  its  organs. 

A  muscle  is  composed  of  bundles  of  muscular  fibres 
which  are  held  together  by  connective  tissue.  Muscles  are 
supplied  with  blood-vessels  and  with  motor  and  sensory 
nerves. 

In  the  higher  developed  animals  we  find  two  varieties 
of  muscular  fibres — viz. ,  the  striated  and  the  non-striated. 
The  minute  structure  of  these  I  have  already  described  in 
my  preliminary  lectures  on  histology. 

The  special  function  and  physiological  property  of 
muscles  is,  first,  their  power  of  moving  their  substance,  pro- 
ducing a  forcible  shortening  of  the  muscle.  This  property  is 
known  as  contractility,  and  the  exhibition  of  this  property 
is  known  as  a  muscular  contraction. 

The  contraction  of  certain  muscles  in  the  body  is  con- 
trolled by  the  will  of  the  individual.  These  are  called  the 
voluntary  muscles,  whereas  those  muscles  which  cannot  be 
contracted  by  an  effort  of  the  will  are  called  the  invol- 
untary muscles.  A  muscle  in  an  animal  body  may  be  in  a 
state  of  rest  or  in  a  state  of  activity.  After  death  the 
muscle  passes  into  a  state  known  as  rigor. 

The  muscle  changes  its  physical,  chemical,  and  electrical 
conditions  as  it  passes  from  one  state  into  another. 


302     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

These  changes  are  due  to  the  metabohc  processes  taking 
place  in  the  muscle;  the  effect  of  these  metabolic  processes 
is  heat  and  labor.  The  changes  taking  place  in  the  muscle 
after  death,  as  it  passes  into  the  state  of  rigor,  must  be  con- 
sidered as  the  result  of  retrogressive  processes. 

To  understand  the  changes  which  take  place  in  muscle 
as  it  passes  from  one  state  into  the  other,  it  is  best  to  con- 
sider the  conditions  of  the  muscles  in  these  states. 

The  Condition  of  Muscles  in  a  State  of  Rest. 

(a)  Physical. — The  muscles  in  the  animal  body  are  at- 
tached with  their  free  ends  to  some  other  anatomical 
structure.  Muscles  are  sHghtly  elastic,  and  they  are  always 
somewhat  stretched  beyond  their  natural  length  between 
their  points  of  attachment,  so  that  a  muscle  has  always 
a  certain  tension.  This  condition  has  for  its  purpose  the 
saving  of  labor.  If  the  muscle  when  in  a  state  of  rest 
should  be  in  a  relaxed  condition,  then  a  certain  amount 
of  muscular  force  would  be  lost  in  making  the  muscle 
tense  between  its  points  of  attachment.  That  such  tension 
exists  in  the  resting  muscle  is  best  shown  by  the  fact  that 
a  muscle,  when  cut,  at  once  shortens  until  it  has  assumed 
its  natural  length. 

(6)  Chemical. — The  reaction  of  living  nmscle  in  a  state 
of  rest  is  neutral  or  slightly  alkaline. 

The  chemical  composition  of  living  muscle  cannot  be  de- 
termined accurately,  as  any  chemical  treatment  which  may 
be  employed  for  an  analysis  causes  death  of  the  muscle. 

Muscle  is  composed  of  75  to  80  per  cent  of  water  and  20 
to  25  per  cent  of  solids;  the  largest  portion  of  the  latter  con- 
sists of  albuminous  substances. 

The  principal  albuminous  ingredient  of  muscle  is  myo- 
sin. It  is  believed  to  be  an  ingredient  of  living  muscle,  be- 
cause it  is  obtained  by  a  process  which  causes  the  least 
chemical  change — namely,  by  freezing  and  a  subsequent 
simple  manipulation. 


ANIMAL   MOTIONS.  303' 

If  a  living  muscle— for  instance,  that  of  the  frog— be 
frozen,  then  divided  minutely  and  the  mass  then  squeezed 
through  a  cloth,  a  turbid,  yellowish  liquid  is  obtained,  called 
the  muscle-plasma.  It  is  alkaline,  and  coagulates  at  or- 
dinary temperature  into  a  clot  and  a  clear,  yellowish  liquid, 
the  muscle-serum. 

The  clot  is  composed  of  the  myosin,  w^hich  has  separated 
from  the  plasma  in  whitish  flakes. 

The  muscle-serum  is  acid,  is  composed  of  water,  inorganic 
salts,  principally  potassium  phosphate,  and  of  organic  in- 
gredients such  as  serum -albumin,  fat,  organic  acids,  glyco- 
gen, dextrose,  inosit,  extractive  substances,  haemoglobin,, 
and  CO,. 

Myosin  is  also  obtained  by  treating  fresh  muscle  with  a 
10  per  cent  solution  of  sodium  chloride. 

Myosin  is  an  organic,  nitrogenous,  albuminous  substance. 
It  is  soluble  in  dilute  saline  and  acidulous  solutions,  and 
readily  coagulable  by  heat  and  alcohol;  with  dilute  hydro- 
chloric acid  it  forms  acid-albumin,  known  as  syntonin. 

An  analysis  of  fresh  muscle  shows  it  to  consist  of  (1)  wa- 
ter, 75  to  80  per  cent;  (2)  myosin,  serum-albumin;  (3)  or- 
ganic nitrogenous  extractive  substances,  such  as  creatin, 
creatinin,  xanthin,  hypoxanthin,  urea;  (4)  carbohydrate 
substances — glycogen,  dextrose,  inosit;  (5)  organic  acids, 
principally  sarcolactic  acid;  (6)  inorganic  substances — 
namely,  potassium  phosphate,  calcium  and  magnesium 
phosphate,  chlorides,  and  traces  of  iron;  (7)  gases — viz., 
C0„,  N,  and  oxygen. 

(c)  Electrical. — It  has  been  observed  that  in  animal  tis- 
sues there  exist  natural  electrical  currents.  It  has  been 
demonstrated  that  these  exist  in  muscle. 

To  E.  Du  Bois-Reymond  must  be  given  the  credit  of  hav- 
ing studied  and  explained  the  subject  of  the  natural  electri- 
cal currents  in  the  animal  tissues,  and  the  laws  governing 
them,  most  precisely  and  minutely.  In  his  many  interesting 
publications  on  electro-physiology  he  describes  the  various 
observations  and  experiments  he  made  in  this  direction. 


304     LECTURES   OX   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

Time  is  too  limited  to  dwell  on  the  subject  more  than  is 
absolutely  necessary. 

For  his  experiments  Reymond  used  a  pair  of  unpolarized 
electrodes,  which  he  connected  with  a  galvanometer. 

To  study  the  electrical  currents  in  muscle,  prismatic 
pieces  are  cut  out  of  the  living  tissue.  Such  a  prism  is  iso- 
lated by  placing  it  on  a  glass  plate,  and  the  electrodes  are 
applied  to  its  various  points;  the  currents  are  indicated  on 
the  galvanometer.  Such  a  muscle  prism  has  a  longitudinal 
and  a  transverse  section.  The  longitudinal  section  runs 
parallel  with  the  long  axis  of  the  muscle  fibres;  the  trans- 
verse section  is  the  transversely  cut  portion.  A  line  pass- 
ing transversely  across  the  middle  of  the  longitudinal 
section  is  termed  the  equator.  If  now  one  of  the  electrodes 
is  applied  to  a  point  on  this  equator,  and  the  other  elec- 
trode to  any  point  distant  from  it,  it  will  be  noticed  that 
an  electric  current  passes  from  the  electrode  on  the  equator, 
through  the  conducting  wire,  to  the  electrode  placed  at  the 
distant  point,  and  from  this  point  through  the  muscle  mass 
to  the  point  at  or  near  the  equator. 

The  point  at  or  nearest  the  equator  is  the  positive  pole; 
the  point  distant  from  the  equator  is  the  negative  pole. 

The  laws  governing  the  electrical  currents  in  muscle,  as 
laid  down  by  Du  Bois-Reymond,  are  as  follows: 

1.  Currents  are  obtained  between  two  points  on  the  lon- 
gitudinal section  of  the  prism,  provided  the  points  are  not 
equally  distant  from  the  equator. 

2.  The  points  nearest  the  equator  are  the  positive,  those 
distant  from  the  equator  are  the  negative,  poles. 

3.  The  greater  the  distance  between  the  two  points  the 
stronger  the  current. 

4.  Currents  between  points  on  the  longitudinal  section 
and  points  on  the  transverse  section  are  the  strongest. 

5.  Currents  between  two  points  on  the  longitudinal  sec- 
tion, or  between  two  points  on  the  transverse  section,  are 
weak. 


ANIMAL   MOTIONS.  305 

6.  Currents  between  two  points  on  the  transverse  sec- 
tion pass  from  the  electrode  most  distant  from  the  middle 
of  the  transverse  section  through  the  wire  to  the  point 
nearest  the  middle  of  the  transverse  section  ;  the  latter 
point  is  the  negative,  the  former  point  the  positive,  pole. 

7.  No  currents  are  obtained  between  two  points  which 
are  equally  distant  from  the  middle  point  of  the  longitudi- 
nal or  from  that  of  the  transverse  section. 

8.  The  strength  of  the  current  decreases  as  the  points 
between  which  it  passes  are  brought  nearer  to  the  middle 
point,  or  equator,  of  the  longitudinal  section. 

2.  The  Condition  of  Muscles  in  a  State  of  Activity. 

(a)  Physical. — The  muscle  changes  its  form  during  con- 
traction ;  the  muscular  fibres  and  the  w^hole  muscle  become 
shorter  and  thickened  without  changing  their  volume. 

(&)  Chemical. — The  activity  of  the  muscle  is  the  result  of 
chemical  processes  taking  place  in  it;  during  these  the 
potential  force  contained  in  the  ingredients  of  the  muscles 
is  transformed  into  living  force — viz.,  heat  and  labor. 

The  chemical  processes  taking  place  in  muscle  during 
its  activity  are  the  dividing  and  oxidizing  of  its  organic  in- 
gredients with  the  production  of  carbon  dioxide,  water, 
and  sarcolactic  acid. 

To  determine  the  chemical  changes  taking  place  in 
muscle  during  activity,  it  is  necessary,  first,  to  produce 
tetanic  contractions,  and,  secondly,  to  cut  off  the  blood- 
supply,  because  the  blood  constantly  supplies  new  materials 
and  carries  off  the  products  of  the  chemical  processes. 

The  chemical  composition  and  condition  of  fresh  teta- 
nized  muscle,  as  compared  with  that  of  muscle  in  a  resting 
state,  is  as  follows  : 

1.  It  is  acid  in  reaction,  due  to  the  increased  quantity  of 
sarcolactic  acid. 

ii.  It  contains  a  smaller  quantity  of  non-nitrogenized  in- 
gredients, such  as  glycogen,  sugar,  fat. 

20 


306     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

3.  It  contains  more  water. 

4.  It  contains  more  CO^. 

5.  The  quantity  of  nitrogenous  ingredients  and  of  ex- 
tractives is  not  materially  decreased  or  increased. 

From  this  description  it  follows  : 

1.  That  CO^,  water,  and  sarcolactic  acid  are  the  products 
of  chemical  changes  in  muscle  during  activity. 

2.  That  glycogen,  sugar,  and  fat — viz.,  non-nitrogenized 
ingredients  of  the  muscle — are  the  principal  sources  of 
these  products.  The  quantity  of  non-nitrogenous  ingre-^ 
dients  in  muscle  is  not  sufficient  to  produce  the  quantity  of 
COj,  etc.,  formed  in  muscle  during  activity,  but  it  must  be 
considered  that  muscle  continually  receives  a  supply  of 
non-nitrogenous  material  with  the  blood;  it  has  also  been 
observed  that  the  quantity  of  glycogen  is  greatly  dimin- 
ished when  the  muscles  of  the  body  are  tetanized. 

3.  That  the  organic  nitrogenous  ingredients  of  muscle 
probably  do  not  enter  to  any  extent  in  the  production  of 
CO2,  water,  and  sarcolactic  acid.  Muscle  in  a  state  of  rest 
contains  a  smaller  quantity  of  organic  nitrogenous  ex- 
tractives, and  it  is  believed  that  the  organic  nitrogenous 
ingredients  of  muscle  merely  partake  in  the  chemical  pro- 
cesses in  the  muscle,  in  that  they  give  off  some  oxygen 
which  is  taken  up  by  the  non-nitrogenous  materials. 

(c)  Electrical. — The  electrical  condition  of  muscle  also 
changes  as  the  muscle  passes  into  the  state  of  activity. 
The  changes  taking  place  have  been  studied  and  observed 
most  accurately  by  E.  Du  Bois-Reyrnond.  He  describes 
them  as  follows : 

1.  The  direction  of  the  current  is  changed. 

2.  The  current  is  weakened,  due  to  the  greater  resistance 
which  is  presented  to  the  current  by  the  shortening  and 
thickening  of  the  muscle  mass. 

During  the  activity  of  muscle  there  take  place  certain 
thermal  processes.  It  is  well  known  that  muscular  activ- 
ity increases  the  body  temperature,  and  v.  Helmholtz  has 


ANIMAL   MOTIONS.  307 

demonstrated  that  during  the  activity  of  a  muscle  heat  is 
produced  as  the  result  of  chemical  processes. 

Heidenliain  has  ascertained,  with  the  use  of  very  sensi- 
tive thermal  apparatus,  that  the  temperature  in  the  muscle 
of  a  frog  is  raised  i^oo"  of  one  degree  C.  during  one  single 
contraction. 

A  peculiar  phenomenon  observed  during  muscular  con- 
traction is  the  muscular  sound.  This  is  a  deep,  dull  sound, 
and  is  easily  heard  by  placing  a  stethoscope  over  the  muscle 
during  its  contraction.  The  sound  consists  of  from  16  to  20 
vibrations,  which  shows  that  a  muscular  contraction  is  not 
continuous  but  interrupted.  A  muscular  contraction  is 
therefore  not  produced  by  one  but  by  a  succession  of  nerve 
stimuli.  The  changes  which  a  muscle  undergoes  in  its 
chemical,  thermal,  and  electrical  conditions,  as  it  passes 
from  a  resting  into  an  active  state,  are  practically  the  same 
in  th©  striated  and  in  the  non-striated  muscles. 


LECTURE    XXXITl. 

THE   ACTIVITY   OF   MUSCLE. 

The  activity  of  a  muscle  consists  in  its  contraction. 

A  muscle  passes  from  the  resting  into  the  active  state 
when  it  receives  a  stimulus.  The  property  of  a  muscle  to 
respond  to  stimuli  is  termed  muscular  irritahiUtij.  Ordi- 
narily a  muscle  in  the  body  receives  the  stimulus  for  its 
contraction  through  its  motor  nerve;  this  is  called  the 
natural  stimulus.  The  muscles  are  supplied  with  motor 
nerves.  The  fibrins'  enter  the  muscular  fibres  and  cells  and 
terminate  in  a  flat,  granular  expansion  known  as  the  nioto- 
rial  end  plate,  from  which  filaments  from  the  axis  cylinder 
radiate  through  the  mass  of  the  muscle  fibre.  The  sarco- 
lemma  of  the  striated  muscular  fibres  becomes  continuous 
with  the  neurilemma  of  the  nerve-fibre  entering  it.  The 
nerve  distribution  to  the  plain  or  non-striated  muscular 
fibres  is  more  complicated. 

The  activity  of  a  muscle  can  also  be  excited  by  chemical, 
mechanical,  thermal,  or  electrical  stimuli.  They  are  called 
artificial  stimuli,  and  they  may  be  applied  directly  to  the 
muscle  or  to  its  motor  nerve. 

Chemical  stimuli  are  those  which  act  by  their  chemical 
properties  to  produce  certain  chemical  changes  in  muscle. 
Such  substances  are  solutions  of  certain  salts,  alkalies  or 
acids,  alcohol,  ether,  and  certain  gases.  If,  for  instance,  the 
motor  nerve  of  a  muscle  is  dipped  into  a  solution  of  sodium 
chloride,  or  of  alkalies  or  acids  of  certain  strengths,  a  mus- 
cular contraction  is  produced.  The  same  effect  is  produced 
when  the  isolated  muscle  itself  is  subjected  to  the  influence 
of  these  solutions. 

Mechanical  stimuli  are  those  produced  by  a  blow,  pres- 


THE    ACTIVITY   OF   MUSCLE.  30& 

sure,  puncture,  or  squeezing  of  the  muscle  or  its  nerve. 
They  produce  their  effect  by  causing  certain  molecular 
changes  in  the  substance  of  the  nerve  or  muscle. 

Tliermal  stimuli  are  produced  by  the  application  of  heat 
and  cold.  It  has  been  observed  that  the  application  of 
heat  or  cold  produces  muscular  contractions. 

The  irritability  of  muscle  is  destroyed  by  the  application 
of  heat  or  cold  beyond  certain  limits. 

Electrical  stimuli.  Muscular  contractions  can  be  pro- 
duced by  the  application  of  electrical  currents.  Both  the 
continuous  and  the  induced  current  may  be  used  to  study 
the  effect  of  electrical  currents. 

If  a  continuous  current  of  an  equal  strength  is  passed 
through  a  muscle  or  applied  to  its  motor  nerve,  no  contrac- 
tion is  produced.  This  effect  is  only  produced  when  the 
strength  of  the  current  is  repeatedly  and  suddenly  changed, 
and  at  the  moments  when  the  current  is  opened  and  closed. 

An  induced  current  is  produced  by  means  of  an  induc- 
tion coil,  by  which  the  current  may  be  interrupted  at  regu- 
lar intervals.  If  such  a  current  is  applied  a  muscular  con- 
traction will  be  produced  at  each  interruption  of  the  current. 
For  the  purpose  of  studying  the  irritability  of  muscles  or 
nerves,  electrical  stimuli  are  preferable,  because  they  pro 
duce  the  least  changes  in  the  substance  of  these  organs 
when  applied  in  moderate  strength,  and  also  because  they 
are  easily  applied  and  can  be  accurately  regulated. 

The  contractility  and  irritability  of  muscle  is  an  inherent 
physiological  and  characteristic  property  of  nmscle  and  is 
not  dependent  on  nerve  influence.  This  has  been  demon- 
strated by  experiments  made  with  curare,  the  Indian  arrow 
poison.  This  is  the  juice  or  resin  of  a  tree  of  the  strychnos 
family.  If  a  very  small  quantity  of  the  poison  is  intro- 
duced into  the  blood  circulation  it  produces  a  paralysis  of 
the  voluntary  muscles  and  brings  about  death  by  the  para- 
lyzation  of  the  respiratory  muscles.  Introduced  into  the 
stomach  it  produces  no  poisonous  effect. 


310     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Curare  does  not  paralyze  the  sensory  and  secretory  nerves, 
nor  the  motor  nerves  of  the  organic  muscles — viz.,  the  non- 
striated  and  cardiac  muscle.  Curare  only  paralyzes  the 
motorial  end  plates  of  the  skeletal  or  striated  voluntary 
muscles.  Poisoning  with  curare  therefore  makes  the  indi- 
vidual unable  to  contract  the  skeletal  muscles;  the  so  para- 
lyzed muscles  do,  however,  respond  to  stimuli  applied  di- 
rectly to  them.  This  demonstrates  that  these  muscles 
possess  the  inherent  pi'operty  of  responding  to  stimuli. 
This  property,  however,  ceases  when  the  muscle  is  paralyzed 
and  inactive  for  a  long  time,  and  the  muscles  in  the  body 
degenerate  when  severed  from  their  nerve  connection. 
Experiments  in  this  direction  have  not  been  made  with  the 
organic  muscles,  as  no  mode  is  known  by  which  their  motor 
nerves  can  be  paralyzed;  but  it  is  supposed  that  they  also 
possess  the  inherent  property  of  responding  to  stimuli  in- 
dependent of  their  nerve  connection.  The  two  varieties  of 
muscles — viz.,  the  skeletal  or  striated  and  the  organic  or 
non-striated  muscles — differ  somewhat  in  their  mode  of  re- 
sponding to  stimuli.  Non  striated  muscles  respond  more 
slowly  to  stimuli.  When  a  stimulus  is  applied  to  a  non- 
striated  muscle  a  contraction  of  the  muscle  begins  at  the 
point  to  which  the  stimulus  is  applied,  and  the  contraction 
gradually  extends  beyond  wiiile  the  portion  first  contracted 
relaxes.  The  effect  of  this  is  the  peculiar  peristaltic  contrac- 
tion of  the  organic  muscles.  The  contraction  of  an  invol- 
untary muscle  continues  for  some  time  after  the  stimulus 
is  withdrawn.  Striated  muscles  respond  quickly  to  stim- 
uli. When  a  stimulus  is  applied  to  a  striated  muscle  an 
instantaneous  contraction  takes  place  in  that  part  of  the 
muscle  to  which  the  stimulus  is  applied;  the  contraction 
ceases  instantaneously  when  the  stimulus  is  withdrawn. 

Application  of  a  succession  of  electrical  stimuli  to  a  non- 
striated  muscle  by  means  of  an  induced  current  produces, 
if  any,  a  slow  contraction  which  alternates  with  periods  of 
rest.     The  application  of  an  induced  current  to  a  striated 


THE   ACTIVITY   OP   MUSCLE,  311 

muscle  produces  a  tetanic  contraction.  Non- striated  mus- 
cles respond  more  forcibly  when  a  continuous  current  is 
applied.  This  is  characteristic  of  the  non- striated  muscles 
in  the  case  of  thermal  stimuli:  application  of  cold  produces 
their  contraction,  warmth  their  relaxation. 

The  fibres  of  the  cardiac  muscle  resemble  the  non-striated 
fibres  in  their  mode  of  contraction  and  in  their  mode  of 
responding  to  stimuli. 

The  rapidity  of  the  contraction  also  varies  in  the  two 
kinds  of  muscles.  When  a  muscle  is  stimulated  the  stimu- 
lus is  conducted  from  particle  to  particle  in  the  muscle;  the 
result  is  that  the  contraction  propagates  from  the  point  to 
which  the  stimulus  is  applied  to  its  various  particles,  pro- 
ducing a  contraction  which  passes  with  a  wave-like  motion 
over  the  whole  organ. 

In  the  striated  skeletal  muscles  the  wave  of  the  contrac- 
tion has  a  rapidity  of  from  10  to  15  metres  per  second;  in 
the  organic — viz.,  the  non-striated  and  the  cardiac  muscle-— 
this  is  much  slower,  namely,  from  10  to  15  millimetres  per 
second. 

The  Muscular  Work. — The  work  which  a  muscle  can  do 
is  the  result  of  its  physiological  activity.  When  a  muscle 
contracts  it  shortens  and  thickens.  The  height  which  a 
muscle  assumes  by  its  thickening  is  proportional  to  its 
shortening.  If  a  muscle  is  loaded  with  a  weight  it  will 
raise  that  weight  to  a  certain  height  by  the  force  of  its 
contraction.  The  amount  of  work  which  is  done  by  a 
muscle  is  estimated  by  multiplying  the  weight  with  which 
the  muscle  is  loaded  by  the  height  to  which  it  is  raised 
in  the  muscular  contraction.  The  amount  of  work  done 
by  a  muscle  is  expressed  in  gramme-millimetres. 

If  A  expresses  the  work  done  by  the  muscle,  P  the 
weight  with  which  the  muscle  is  loaded,  and  B  the  height 
to  which  that  weight  is  raised,  then  the  calculation  is  as 
follows  :  A  =  P  multiplied  by  B.  Thus,  if  a  muscle  raises 
a  weight  of  5  grammes  to  a  height  of  27.6   millimetres, 


312      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

then  the  work  done  by  that  muscle  equals  138  gramme- 
millimetres. 

The  height  to  which  a  muscle  rises  by  thickening  is 
greatest  when  a  maximal  stimulus  is  applied  and  when 
the  muscle  is  not  loaded  by  a  weight. 

The  results  of  many  observations  and  experiments  made 
to  explain  the  laws  regulating  the  muscular  work  are 
principally  the  following  : 

1.  When  a  muscle  is  not  loaded  with  any  weight  as  it 
contracts,  then  the  work  done  by  the  same  equals  0. 

2.  When  the  weight  with  which  the  muscle  is  loaded  is 
so  great  that  the  muscle  cannot  contract — viz.,  that  it  can- 
not shorten  and  thicken,  and  consequently  cannot  raise  the 
weight — then  the  muscle  does  no  work. 

3.  The  work  done  by  a  muscle  increases  and  decreases 
as  the  stimulus  is  decreased  or  increased,  within  certain 
limits. 

4.  The  height  to  which  a  muscle  raises  a  weight  with 
which  it  is  loaded  decreases  as  the  weight  increases. 

5.  The  greater  the  physiological  transverse  section  of  a 
muscle,  the  greater  the  weight  it  can  raise. 

6.  The  longer  a  muscle  the  greater  the  height  to  which 
it  can  raise  a  weight. 

T.  The  elasticity  of  a  muscle  must  be  considered  an  im- 
portant factor  of  the  muscular  work. 

8.  The  absolute  ivork  or  power  of  a  muscle  is  that  done 
by  a  muscle  when  a  maximum  stimulus  is  applied,  and 
when  it  is  loaded  with  as  much  weight  as  it  can  raise  with- 
out stretching. 

9.  A  muscle  becomes  stronger  by  repeated  and  moderate 
work. 

10.  A  muscle  becomes  fatigued,  and  finally  exhausted, 
when  overtaxed  either  by  long-continued  or  too  great 
work. 

Muscular  fatigue  is  a  condition  indicated  by  a  gradual 
decrease  of  the  work  the  muscle  is  capable  of  doing. 


THE  ACTIVITY  OP  :virscLE.  313 

It  is  believed  tiiat  the  condition  is  due  to  tlie  accumula- 
tion of  the  products  of  the  metabolic  processes  in  the  mus- 
cle. Muscle  recovers  from  its  fatigued  condition  T\'hen 
these  products  are  removed:  ordinarily  this  is  effected  by 
the  circulation. 

III.    TJie  Conditions  of  the  Muscle  in  a  State  of  Rigor. 

The  rigor  of  the  muscle  is  a  condition  which  is  caused 
whenever  the  nutrition  of  the  muscle  and  its  metabolic 
processes  are  interfered  with. 

In  the  condition  of  rigoi'  the  muscle  has  lost  all  its 
physiological  properties  and  is  characterized  by  changes 
in  its  physical,  chemical,  and  other  conditions. 

(a)  Changes  in  the  Physical  Condition.- — The  muscle 
loses  its  fresh  red  color  and  becomes  whitish  and  opaque; 
it  becomes  stiff  and  firm  and  loses  its  elasticity. 

(6)  Changes  in  the  Chemical  Condition. — The  reaction 
is  acid,  due  to  the  increased  amount  of  sarcolactic  acid. 
There  is  a  coagulation  of  albuminous  ingredients  of  the 
muscle  plasma,  by  which  the  peculiar  stiffening  is  pro- 
duced. 

(c)  Changes  in  the  Electrical  Condition. — There  exist  no 
natural  electrical  currents  in  a  muscle  in  a  state  of  rigor. 

Muscular  rigor  is  characterized  by  a  peculiar  contraction 
of  the  muscles.  This  produces  -the  condition  known  as 
rigor  mortis,  which  is  observed  in  bodies  after  death.  It 
begins  from  two  to  seven  hours  after  death,  and  continues 
for  two  or  three  days.  During  that  time  the  contraction 
of  the  muscles  produces  the  peculiar  stiff^ening  and  conse- 
quent inability  to  bend  the  joints  in  the  dead  during  that 
period.  Eigor  mortis  subsides  after  two  or  three  days, 
owing  to  the  beginning  of  the  decomposition  of  the  muscle 
substance. 

TJie  Function  of  the  Involuntary  Muscles. 
The   involuntary   muscles  generally  have  no   bony   at- 


314     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

tachment,  but  they  form  the  walls  of  certain  hollow  organs, 
as  the  heart,  intestines,  bladder,  uterus,  etc. 

The  function  of  the  involuntary  muscles  is  to  produce 
the  diminution  of  the  hollow  organs.  The  peculiar  mode 
of  activity  and  contraction  is  due  to  the  more  or  less  com- 
plicated nerve  termination  and  distribution  in  muscles. 

The  Function  of  the  Voluntary  Muscles. 

The  voluntary  muscles  are  principally  the  skeletal 
muscles.  They  are  attached  to  the  bones  in  such  a  manner 
that  in  the  simplest  form  the  muscle  passes  from  one  bone 
to  another,  and  thus  effects  by  its  contractions  the  motions 
of  the  joints  between  the  bones.  The  motions  of  the  joints 
are  effected  in  a  manner  similar  to  the  actions  of  a  lever; 
the  axis  of  motion  or  fulcrum  is  the  joint,  the  power  re- 
moving the  weight  is  the  muscular  action,  and  the  weight 
to  be  removed  is  the  resistance  offered  to  the  bone  to  be 
moved  in  the  joint.  There  exist  three  varieties  of  levers;  all 
three  are  represented  in  the  human  body.  The  difference 
between  the  various  levers  is  made  according  to  the  differ- 
ence in  the  relative  positions  of  the  power,  fulcrum,  and 
weight. 

The  skeletal  muscles  are  therefore  the  active  organs  for 
the  motions  and  locomotions  of  the  body. 

Standing,  walking,  running,  leaping,  and  jumping  are  all 
acts  for  the  performance  of  which  nearly  every  voluntary 
muscle  is  brought  into  play  to  a  greater  or  less  degree. 

11.  Ciliary  Motion. 

Ciliary  motion  is  the  peculiar  motion  possessed  by  the 
minute  hair-like  protoplasmic  processes  of  the  ciliated  cells. 
Such  cells  are  found  covering  the  mucous  membrane  of  the 
respiratory  passages,  of  the  Eustachian  tube,  the  Fallopian 
tubes,  and  the  vasa  efferentia.  The  motion  of  the  cilia  in 
these  regions  is  from  within  outward,  and  has  for  its  object 
the  preventing  of  the  entrance,  and  favoring  the  exit,  of 
substances  from  these  localities.     For  instance,  the  ciliary 


QUESTIONS   AND    EXERCISES,  315 

motion  of  the  epithelial  cells  covering  the  respiratory  tract 
has  for  its  object  the  removal  of  mucus  and  inhaled  par- 
ticles of  foreign  matter,  such  as  dust,  germs,  etc.  The 
cihated  epithehum  covering  the  hning  of  the  Fallopian 
tubes,  by  the  motion  of  its  cilia,  aids  the  passage  of  the 
matured  ovum  into  the  uterus. 

The  motion  of  the  cilia  of  the  cells  covering  a  surface 
is  rapid  and  wavy  and  in  a  certain  direction. 

The  motion  of  the  cilia  of  a  cell  is  not  dependent  upon 
nerve  influence.  If  a  cell  is  removed  from  the  body  the 
motion  of  its  ciha  can  be  observed  for  some  time.  It  is 
very  likely  that  the  motion  of  the  ciha  is  caused  by  stimuH 
from  the  cell-body. 

Electrical  currents,  weak  alkahne  solutions,  and  a  mode- 
rate rise  of  temperature  favor  cihary  motion;  cold,  great 
heat,  solutions  of  acids,  and  CO.,  destroy  the  same. 

The  motions  of  the  delicate  filaments  of  the  body  of  the 
spermatozoon  must  also  be  regarded  as  a  motion  similar  to 
the  motion  of  the  cilia. 

III.  Protoplas^hc  Motion. 

The  best  example  of  protoplasmic  motion  is  the  amoe- 
boid motion  of  the  leucocytes,  by  which  they  migrate  in 
the  system,  and  by  which  they  take  up  into  their  body  par- 
ticles of  substances. 

The  Bronmian  movement  of  particles  in  the  protoplasm 
of  cells  is  probably  caused  by  a  molecular  motion  of  the 
protoplasm.  

QUESTIONS   AND   EXERCISES. 

Subject. — Animal  Heat  and  Animal  Motions.     Uie  Physi- 
ology of  Muscle. 
Lectures  XXXI.-XXXIII.  inclusive. 

Animal  Heat. 

639.  What  is  meant  by  kinetic  force — potential  force — 
latent  heat  ? 

640.  Define  animal  heat. 


316     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

6il.  What  is  meant  by  homoiothermal  animals  ? 
642.  What  is  meant  by  poikilothermal  animals  ? 
6-i3.  What  is  the  average   normal   temperature   of  the 
healthy  adult  ( 

644.  Give  the  sources  of  animal  heat. 

645.  How  is  the  quantity  of  heat  ascertained  which  is 
produced  by  the  combustion  of  substances  ? 

646.  What  is  meant  by  one  heat-unit  ? 

647.  Describe  the  water  calorimeter. 

648.  What  is  the  total  quantity  of  heat-units  produced 
in  twenty-four  hours  in  the  body  of  a  healthy  adult  who 
takes  a  normal  mixed  diet  '. 

649.  How  is  heat  eliminated  from  the  body  i 

650.  Give  the  percentage  of  heat  eliminated  in  various 
ways. 

651.  How  is  the  body  temperature  regulated  ? 

652.  Wliat  is  meant  by  fever  ? 

653.  Who  invented  the  thermometer  ? 

654.  Name  the  difference  in  the  various  scales  of  the 
thermometers,  and  give  the  normal  temperature  of  the 
human  body  on  the  various  scales. 

655.  Explain  the  method  of  converting  the  various  scales 
one  into  the  other. 

656.  What  is  the  preferable  way  of  taking  the  body 
temperature,  and  why  i 

657.  Name  diseases  in  which  a  subnormal  temperature 
may  be  found. 

65S.  How  does  the  temperature  compare  with  the  num- 
ber of  pulsations  and  with  the  number  of  respirations  'i 

659.  What  is  the  temperature  curve  in  remittent,  and 
what  is  it  in  intermittent  fever,  and  name  a  type  of  each. 

660.  What  is  the  quantity  of  heat-units  produced  by  the 
combustion  of  one  gramme  of  each  of  the  following  :  car- 
bon, hydrogen,  albumen,  fat,  carbohydrates  i 

661.  Is  the  combustion  of  albumens  in  the  animal  body 


QUESTIONS   AND   EXERCISES.  317 

complete  ?    If  not,  what  is  the  ultimate  product  of  their 
combustion  ? 

662.  What  is  the  quantity  of  heat-units  produced  by 
the  combustion  of  one  gramme  of  urea  ? 

Animal  Motions. 

663.  Name  the  varieties  of  animal  motions. 

664.  What  is  the  physiological  property  of  muscle  ? 

665.  Name  the  states  in  which  muscle  may  exist. 

666.  Name  the  chemical  and  physical  and  electrical  con- 
ditions of  muscles  in  a  state  of  rest. 

667.  Name  the  changes  in  the  physical,  chemical,  and 
electrical  condition  in  a  muscle  as  it  passes  from  a  resting 
into  the  active  state. 

668.  What  do  you  understaad  by  the  muscular  sound  ? 
Explain. 

669.  What  do  you  understand  by  muscular  irritability  ? 
How  may  it  be  excited,  and  what  is  the  natural  stimulus  ? 

670.  What  do  you  understand  by  muscular  work,  mus- 
cular fatigue  ?    Give  cause  of  the  latter  condition. 

671.  What  do  you  understand  by  muscular  rigor  ? 

672.  What  changes  take  place  in  muscle  in  that  con- 
dition ? 

673.  What  is  the  function  of  (a)  the  voluntary,  and  of  {h) 
the  involuntary  muscles  ? 

674.  What  is  the  effect  of  the  introduction  of  curare  into 
the  blood  circulation  ? 

675.  Define  clonic  and  tonic  contraction. 

676.  What  is  tetanus  ?    Trismus  ?    Epilepsy  ? 

677.  What  do  you  understand  by  ciliary  motion  ? 

678.  Give  example  of  protoplasmic  motion. 


LECTURE    XXXIT. 

THE   PHYSIOLOGY   OF   THE    NERVOUS   SYSTEM. 

I.    The  General  Structure  of  the  Organs  of  the  Nervous 
System  and  their  General  Functions. 

The  nervous  system  of  the  human  body  consists  of  two 
great  divisions — viz.,  the  cerebrospinal  and  the  sympa- 
thetic nervous  system. 

The  organs  composing  the  cerebrospinal  nervous  system 
are  : 

1.  The  central  organs,  viz.,  the  brain  and  S2:)inal  cord, 
which  contain  as  their  essential  structure  the  nerve-centres. 

The  organs  composing  the  sympathetic  nervous  system 
are: 

1.  The  ganglia,  which  are  its  central  organs,  containing 
the  centres. 

2.  The  nerves  which  connect  these  centres  and  pass  to 
and  from  them. 

A.    The  General  Structure  of  the  Central  Organs  of  the 
Nervous  System. 

The  central  organs  of  the  nervous  system  are  composed 
of  two  structures,  called  the  gray  and  the  white  nerve  sub- 
stance. 

TTie  Gray  or  Vesicular  Nerve  Substance. — This  structure 
has,  as  the  name  implies,  a  grayish  color.  It  is  composed 
of  nerve-cells,  delicate  fibrillee,  and  of  a  mass,  called  the 
neuroglia,  which  supports  these  elements. 

The  nerve-cells,  nerve-vesicles,  or  ganglionic  cells  are 
composed  of  a  reddish,  granular  protoplasm.     They  have 


THE    PHYSIOLOGY    OF    THE    NERVOUS    SYSTEM.  319 

no  distinct  cell-wall,  but  a  clear,  round  or  oval  nucleus, 
with  one  or  more  nucleoli.  The  nerve-cells  are  from  g-Lj- 
to  ^  of  a  millimetre  in  diameter,  and  are  either  oval,  an- 
gular, or  stellate  in  form.  They  have  one,  two,  or  several 
protoplasmic  projections  from  their  body,  which  are  called 
the  jjoles ;  and  nerve-cells  are  called,  accordiDgly,  imi-,  hi-, 
or  multijDoIar  nerve-cells.  These  poles  either  terminate  in 
a  point,  or  anastomose  with  poles  of  other  nerve-cells,  or 
are  continuous  as  the  axis-cylinder  of  a  nerve-fibre. 

The  second  histological  elements  of  the  gray  nerve  sub- 
stance are  the  delicate  non-meduUated  nerve-fihrillce  which 
connect  the  nerve-cells. 

The  nerve-cells  and  the  fibrilla?  connecting  them  are  em- 
bedded in  a  soft,  homogeneous  mass  called  neuroglia.  This 
consists  of  COD nective- tissue  fibres  of  special  cells,  the 
glia  cells,  and  of  a  gelatinous  intercellular  substance. 

The  White  Nerve  Substance  of  the  Central  Organs. — This 
structure  has,  as  the  name  implies,  a  whitish  color.  It 
consists  of  nerve-fibrilla^  which  are  composed  of  the  con- 
tinuation of  the  poles  of  the  nerve-cells  in  the  gray  sub- 
stance. These  fibrillae  are  surrounded  by  a  soft  mass,  the 
medullary  sheath  ;  like  the  fibrillge  iu  the  gray  substance, 
these  are  surrounded  by  neurilemma. 

The  essential  elements  of  the  ceiitral  organs  of  the  ner- 
vous system  are  the  nerve  centres. 

Tlie  Nerve-Centres,  their  Distribution,  and  their  General 
Functions  and  Properties. — According  to  their  distribution, 
the  nerve-centres  or  ganglia  are  divided  into  : 

1.  Central  ganglia — those  contained  in  the  central  or- 
gans. 

2.  Spinal  ganglia — those  interposed  in  the  course  of  the 
peripheral  nerves  of  the  cerebro-spinal  nervous  system. 

3.  Sympathetic  ganglia — the  centres  of  the  sympathetic 
nervous  system. 

The  ganglia  or  nerve-centres  are  either  simple  stellate 
nerve-cells,  like  the  central  ganglia,  or  they  are  more  com- 


320      LECTURES   ON    HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

plicated  in  structure,  like  the  sympathetic  ganglia,  which 
generally  consist  of  pear  shaped  unipolar  nerve-cells,  the 
pole  of  which  is  continuous  as  the  axis-cylinder  of  a 
nerve-fihre;  delicate  fibrillae  from  the  body  of  the  cell  form 
a  second  fibre,  which  passes  spirally  around  the  pole  of  the 
cell.  The  spinal  ganglia  are  sometimes  unipolar  and  some- 
times bipolar  cells. 

The  General  Functions  of  the  Nerve-Centres  dive:  1.  The 
transmission  of  impulses  to  the  nerves   arising  from  them. 

2.  The  reception  of  impulses  from  the  periphery  through 
the  nerves  arising  from  them. 

3.  The  transmission,  to  the  nerves  passing  from  them  to 
the  periphery,  of  the  impulses  which  they  have  received 
through  the  nerves  from  the  periphery.  This  process  is 
termed  a  reflex,  and  the  resulting  physiological  act  is  called 
a  reflex  act. 

Their  Special  Functions. — The  nerves  which  conduct  im- 
pressions from  the  periphery  to  the  centre  are  (a)  the 
nerves  of  sensation  and  (6)  the  sensory  nerves.  The  centres 
receiving  these  impressions  are  called  (a)  the  sensory  centre 
and  (6)  the  sensible  centres. 

The  nerves  conducting  impressions  from  the  centre  to 
the  periphery  are  (a)  the  motor  nerves,  (b)  the  secretory 
nerves,  (c)  the  inhibitory  nerves,  and  (cZ)  trophic  nerves. 
The  centres  from  which  these  nerves  receive  their  impres- 
sions are  called  (a)  motor  centres,  (6)  secretory  centres,  (c) 
inhibitoi^y  centres,  and  {cl)  trophic  centres. 

According  to  their  special  functions  the  nerve-centres 
are  therefore  divided  into 

1.  Sensory. 

2.  Sensible. 

3.  Motor. 

4.  Secretory. 

5.  Inhibitory. 

6.  Trophic. 

7.  Special  centres  which  govern  psychical  activity^ 


THE   PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM.  331 

The  various  nerve-functions  are  distributed  to  the  vari- 
ous nerve-centres;  none  of  these  can  preside  over  more 
than  one  function. 

The  Geyieral  Properties  of  the  Nerve- Centres. — The  activ- 
ity of  the  motor  centres — viz.,  those  centres  which  transmit 
impulses  to  the  periphery — is  excited  in  various  ways; 
these  are: 

1.  A  motor  centre  may  act  automatically — that  means, 
without  any  nerve  influence  from  without.  The  automatic 
activity  of  a  motor  centre  may  be  continuous,  or  tonic,  or 
intermittent,  or  rhythmical. 

2.  The  activity  of  a  motor  centre  may  be  excited  by  an 
effort  of  the  will — that  means,  it  may  be  voluntary. 

3.  The  activity  of  a  motor  centre  may  be  excited  by  a 
stimulus  received  through  a  nerve  from  the  periphery,  the 
impulse  being  then  reflected  by  the  centre  to  a  motor  nerve. 
This  process  is  termed  rejlex  activity. 

According  to  the  mode  in  which  the  activity  or  impulse 
was  produced  in  the  centre,  we  distinguish: 

(a)  Automatic  and  reflex  secretion. 

(6)  Automatic  and  reflex  inhibition. 

(c)  Automatic,  voluntary,  and  reflex  motion. 

The  various  actions  in  the  body  are  therefore  caused 
either  by  an  automatic,  a  voluntary,  or  a  reflex  activity  of 
the  nerve-centres  presiding  over  the  respective  functions. 

The  nervous  mechanism  for  an  automatic  act  consists  of 
the  nerve-centre  and  the  nerve  passing  from  it  to  the 
periphery. 

The  nervous  mechanism  for  a  voluntary  act  includes  a 
normal  condition  of  the  nerve-centres  which  preside  over 
the  psychical  activity,  the  nerve-centres  presiding  over  the 
respective  function,  and  a  nerve  passing  from  the  centre  to 
the  periphery. 

The  nervous  mechanism  for  a  reflex  act  consists  of  a 
centripetal  nerve  which  conducts  the  impulse  to  the  centre 
from  the  periphery;  the  centre  which  receives  and  reflects 
21 


322     LECTURES   ON   HUMAN  PHYSIOLOGY   AND   HISTOLOGY. 

the  impulse  to  a  centrifugal  nerve;  and  the  latter,  which 
conducts  the  impulse  from  the  centre  to  the  periphery. 

A  reflex  act  is  in  itself  an  involuntary  act,  but  many  of 
the  reflex  acts  in  the  body  are  under  the  control  of  the  will 
— viz.,  they  can  be  altered,  directed,  inhibited,  and  induced 
by  an  effort  of  the  will.  Reflex  acts  may  be  direct  or  in- 
direct. A  direct  reflex  act  is  one  produced  as  the  imme- 
diate result  of  a  peripheral  irritation;  an  indirect  i^eflex 
act,  or  a  secondary  reflex  act,  is  one  which  began  by  an 
effort  of  the  will — viz.,  as  a  voluntary  act — but  it  continued 
involuntarily,  to  be  finally  stopped  again  or  altered  by  the 
will.  Such  acts  are  walking,  writing,  the  climbing  of  stairs, 
etc.  These  are  motions  which  are  started  voluntarily,  but 
continued  involuntarily  without  any  special  voluntary  ef- 
fort. 

Reflex  motions  may  be  simple  or  co-ordinated.  Simple 
reflex  motions  are  merely  the  purposeless  contractions  of 
one  or  several  muscles,  caused  by  the  reflex  activity  of  a 
motor  centre  as  the  result  of  a  peripheral  irritation. 

The  muscular  contractions  in  convulsions,  tetanus,  hydro- 
phobia, and  epilepsy  are  examples  of  simple  reflex  motions. 

Co-ordinated  reflex  motions  are  those  which  are  produced 
when  the  impulse  received  by  the  motor  centre  or  centres 
through  centripetal  nerves  is  reflected  upon  the  motor 
nerves  of  groups  of  muscles,  the  contraction  of  which 
causes  motions  which  are  intended  for  a  certain  purpose. 
If,  for  instance,  during  sleep  the  sole  of  the  foot  is  tickled, 
the  foot  is  drawn  up  as  the  result  of  a  reflex  motion  hav- 
ing for  its  purpose  the  withdrawal  of  the  foot  from  the  ir- 
ritation. 

The  reflex  actions  occurring  normally  in  the  animal  body 
may  be  classified,  in  accordance  with  their  nervous  mech- 
anism, as  follows: 

1.  Those  in  which  the  centripetal  and  centrifugal  nerves 
are  both  cerebro-spinal.  Examples:  coughing,  sneezing, 
deglutition. 


THE   PHYSIOLOGY   OF    THE   NERVOUS    SYSTEM.  323 

2.  Those  in  which  the  centripetal  is  a  cerebro-spinal 
nerve,  and  the  centrifugal  a  sympathetic  nerve.  Example: 
salivary  secretion. 

3.  Those  in  which  both  the  centripetal  and  centrifugal 
nerves  are  sympathetic  nerves.  Example:  the  normal 
mode  of  the  secretion  of  the  gastro-intestinal  juices. 

In  some  abnormal  conditions  the  centripetal  nerve,  which 
conveys  the  stimulus  or  impulse  indirectly  to  the  centre,  is 
a  sympathetic,  and  the  centrifugal  a  cerebro-spinal,  nerve. 
Example:  cramps,  the  spasmodic  muscular  contractions 
of  the  gastro-intestinal  walls,  produced  by  the  injection  of 
substances  which  irritate  the  gastro-intestinal  mucous 
membrane  and  its  sensory  nerves.  Aside  from  the  general 
properties  of  the  nerve-centres  w^hich  I  have  already  de- 
scribed, they  also  possess  the  property  of  conducting,  trans- 
ferring, augmenting,  and  inhibiting  inipulses  which  they 
receive. 

By  the  property  of  conduction  is  understood  the  property 
of  a  nerve-centre  by  which  it  can  conduct  to  another  centre 
impulses  which  it  has  received  through  a  centripetal  nerve. 
If,  for  instance,  food  is  introduced  into  the  gastro-intesti- 
nal canal,  its  presence  irritates  the  sensory  nerves  of  the 
mucous  membrane;  the  impulse  is  conveyed  by  these 
sensory  nerves,  w^hich  are  of  the  sympathetic  plexus,  to  the 
sympathetic  ganglia,  and  it  is  reflected  by  these  upon  the 
motor  and  secretory  fibres  of  the  gastro-intestinal  canal; 
the  result  is  reflex  secretion  and  reflex  motion. 

If,  now,  a  substance  is  introduced  with  the  food  into  the 
intestinal  canal  which  greatly  irritates  the  sensory  fibres  of 
the  mucous  membrane,  then  the  impulse  is  conveyed  by  the 
sensory  nerve  to  the  sympathetic  ganglion  or  centre,  and  it 
is  conducted  by  this  to  centres  more  distant — viz.,  to  those 
of  the  spinal  cord  and  brain;  the  result  is  painful  cramps. 

The  property  of  transference  consists  in  the  capability  of 
nerve-centres  to  transfer  impulses  not  only  to  nerve-fibres 
which  arise  from  them,  but  also  to  adjacent  nerve-fibres. 


324       LECTURES   ON   HUMAN   PHYSIOLOGY  AND   HISTOLOGY. 

Ordinarily  an  impulse  received  by  a  nerve-fibre  at  the  per- 
iphery is  conducted  by  the  same  uninterruptedly  to  the 
centre.  If,  however,  a  nerve-centre  is  interposed  in  the 
course  of  the  fibre  conducting  the  impulse,  then  the  same 
may  be  transferred  by  that  centre  to  an  adjacent  nerve 
fibre,  and  the  impulse  is  then  carried  centrally  by  that 
nerve-fibre. 

An  example  of  this  property  of  nerve-centres  is  the  pain 
in  the  knee-joint  experienced  as  a  symptom  of  hip-joint 
disease.  The  disease  of  the  hip- joint  produces  an  irritation 
of  its  sensory  fibres  by  which  the  impulse  is  conducted 
toward  the  centres  from  which  they  arise.  In  the  course 
of  these  fibres  there  is  interposed  a  centre  or  centres  by 
which  the  impulse  is  transferred  to  adjacent  fibres — which 
in  this  instance  are  sensory  fibres  of  the  knee-joint— and 
the  impulse  is  then  conducted  by  these  to  the  centres  from 
which  they  arise;  the  result  is  the  experience  of  pain  in  the 
knee-joint  instead  of  the  hip-joint. 

By  the  property,  of  augmentation  is  meant  the  property 
possessed  by  nerve-centres  by  which  they  can  increase  a 
stimulus  or  impulse  which  they  have  received. 

By  the  property  of  inhibition  is  meant  the  property  of 
nerve-centres  by  which  they  can  diminish  or  entirely  inhi- 
bit an  impulse  which  they  have  received. 

From  the  foregoing  description  of  the  functions  and  of 
the  properties  of  nerve-centres,  we  may  recapitulate  as 
follows  : 

1.  The  functions  of  the  nerve-centres  are  to  produce  (by 
their  activity)  motion,  secretion,  inhibition,  sensation,  and 
sensibility.  A  nerve-centre  presides  over  only  one  of  these 
functions. 

2.  The  properties  of  the  nerve-centres  are  :  A  nerve- 
centre  may  act  automatically,  voluntarily,  reflexively, 
and  it  may  transfer,  conduct,  augment,  or  inhibit  nerve- 
impulses.  A  nerve-centre  may  possess  more  than  one  of 
these  properties. 


LEOTUEE    XXXV. 

B.     THE   GE^^:RAL   STRUCTURE   OF   THE   >'ERVES. 

A  N'ERVE-TRuyK  is  composed  of  nerve-fibres.  These  are 
held  together  in  bundles  by  connective  tissue  which  passes 
between  the  individual  fibres  and  then  surrounds  the 
bundle.  A  number  of  these  are  again  surrounded  by  con- 
nective tissue,  forming  a  nerve-trunk.  The  connective 
tissue  which  passes  in  between  the  nerve-fibres  is  called 
the  endoneurium ;  that  surrounding  the  bundles  of  nerve- 
fibres  is  called  the  perineurium ;  and  that  holding  the 
bundles  together  is  called  the  epineurium.  These  various 
connective-tissue  structures  are  continuous  with  each 
other.  The  whole  nerve-trunk  is  covered  by  the  nerve- 
sheath. 

The  Structure  of  the  Nerve-Fibres. 

Nerve-fibres  differ  in  their  structure,  and  are  accordingly 
classified  into  meduUated  and  non-medullated  nerve-fibres. 

A  raedidlatecl  nerve-fibre  consists  of  three  structures — 
viz.,  (ci)  an  axis-cylinder,  (6)  the  medullary  sheath,  and  (c) 
the  neurilemma. 

(a)  The  axis-cylinder  is  the  central  portion  and  the 
essential  element  of  a  nerve-fibre;  it  is  of  a  gray-reddish 
color  and  consists  of  delicate  fibrillae.  The  axis-cylinder 
is  continuous  with  a  pole  of  a  nerve-cell  ;  it  passes  in  an 
uninterrupted  course  from  its  origin  to  its  termination, 
and  does  not  branch.  The  axis-cyUnder  is  the  conducting 
p)ortion  of  a  nerve-fibre. 

(&)  The  medullary  sheath,  also  called  the  myelins 
sheath    or   white   substance  of  Schwann,  is  a  semi-sohd, 


326     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

soft,  fatty  substance  which  surrounds  the  axis-cyUnder; 
its  thickness  varies  in  the  various  nerve-fibres. 

(c)  The  neurilemma  is  a  dehcate  tubular  fibrous  sheath 
which  surrounds  as  the  external  covering  many  nerve- 
fibres.  In  it  are  seen,  at  irregular  intervals,  large  oval 
nuclei  surrounded  by  protoplasmic  masses.  These  bodies 
are  called  the  nerve-corpuscles;  they  are  believed  to  be 
remnants  of  f cetal  life. 

Not  all  medullated  nerve-fibres  are  surrounded  by  neuri- 
lemma. It  is  absent  in  the  nerve  fibres  in  the  central 
organs  and  in  those  of  some  nerves  of  special  sense.  It  is 
also  wanting  in  some  fibres  of  the  sympathetic  nerves. 

Those  nerve-fibres  which  are  surrounded  by  neurilemma, 
as  are  all  those  of  the  cerebro-spinal  and  most  of  the  sym- 
pathetic nerves,  present  a  varicosed  or  nodulated  appear- 
ance. This  is  due  to  constrictions  of  the  neurilemma  by 
which,  at  certain  irregular  intervals,  the  continuance  of 
the  medullary  sheath  is  interrupted.  The  nodules  pro- 
duced by  this  peculiar  arrangement  are  called  the  nodes  of 
Banvier.  Medullated  nerve-fibres  which  have  no  neuri- 
lemma do  not  have  this  nodulated,  varicosed  appearance. 

A  non-medullated  nerve-fibre  differs  from  the  former  in 
that  its  axis-cylinder  is  not  surrounded  by  a  medullary 
sheath;  it  consequently  has  a  darker  color.  The  non-me- 
dullated nerve-fibres  of  the  central  organs  are  not  sur- 
rounded by  neurilemma. 

The  Oenercd  Functions  and  Properties  of  Nerve- Fibres. 

The  general  function  of  nerve-fibres  is  the  conduction  of 
impulses.  Nerve-fibres  conducting  impulses  from  the  per- 
iphery to  a  centre  are  called  afferent  or  centripetal  nerves. 

Nerves  conducting  impulses  from  a  centre  to  the  per- 
iphery are  called  efferent  or  centrifugal  nerves. 

Nerves  conducting  impulses  between  centres  are  called 
intercentral  nerves.  The  specicd  function  of  nerve-fibres  is 
the  conduction  of  impulses  of  a  special  character,  and  the 


THE   GENERAL   STRUCTURE    OF   THE   NERVES.  327 

various  Derve-fibres  are  named  accordingly.  The  centrifu- 
gal nerves  are,  according  to  the  character  of  the  impulse 
they  conduct,  divided  into  motor,  secretory,  trophic,  and 
inhibitory  nerves. 

The  centripetal  nerves  are  divided,  according  to  the  cha- 
racter of  the  impulse  which  they  conduct,  into  nerves  of 
special  sense  and  sensory  nerves. 

The  lavi^s  defining  and  explaining  the  conduction  of  im- 
pulses in  nerve-fibres  are,  in  the  principal  points,  the  fol- 
lowing: 

1.  Nerve-fibres  normally  conduct  impulses  only  in  one 
direction. 

2.  The  direction  of  the  current  of  an  impulse  through  a 
nerve-fibre  is  always  longitudinal.  The  current  is  isolated 
and  never  transmitted  laterally. 

3.  A  nerve  fibre  only  conducts  impulses  of  one  kind.  A 
motor  nerve  only  conducts  motor  impulses;  a  sensory 
nerve,  sensory  impulses,  etc. 

4.  The  current  is  transmitted  from  particle  to  particle  of 
the  nerve-substance. 

The  rapidity  of  the  conduction  of  impulses  through 
nerves  was  formerly  believed  to  be  unmeasurable,  but 
Helmholtz  succeeded  in  demonstrating,  with  the  use  of  deli- 
cate apparatus,  that  an  impulse  in  the  motor  nerve  of  a  frog 
is  conducted  with  the  velocity  of  26.4  metres  per  second. 
Experiments  made  in  this  direction  on  the  human  sub- 
ject showed  that  the  velocity  of  the  conduction  of  impulses 
through  motor  and  sensory  nerves  is  from  30  to  60  metres 
per  second. 

The  cause  of  the  activity  of  nerve-fibres  is  the  metabolic 
processes  taking  place,  which  result  in  the  transformation 
of  the  potential  or  latent  forces  contained  in  the  chemical 
ingredients  into  living  or  kinetic  forces. 

The  activity  of  nerve-fibres  is  also  accompanied  by  chem- 
ical changes. 

Nerve-fibre  in  a  resting  state  has  an  alkaline,  and  in  the 


328     LECTURES    ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

active  state  an  acid  reaction;  this  is  due  to  the  formation 
of  lactic  acid. 

Tlie  general  properties  of  nerve-tibres  are:  1.  The  pro- 
perty of  responding  to  stimuli;  it  is  described  as  the  ner- 
vous irritability. 

2.  The  property  of  inherent  natural  electrical  currents. 

1.  Nervous  Irritability. — Xerves  possess,  like  muscles,  the 
property  to  respond  to  agents  which,  when  applied,  excite 
their  activity.  Such  agents  are  called  stimuli,  and  the 
property  of  nerves  to  respond  to  them,  nervous  irritability. 

The  same  agents  which  act  as  stimulants  to  muscles  also 
excite  the  activity  of  nerves. 

The  agents  which  ordinarily  excite  the  activity  of  nerves 
are  called  natural  or  physiological  nerve  stimuli:  their 
exact  nature  is  not  fully  understood. 

Artificial  nerve  stimuli  are  agents  which  excite  nerve  ac- 
tivity when  the  nerve  is  subjected  to  their  influence.  They 
may  be  classified  into  mechanical,  thermal,  and  electrical 
agents.  They  all  produce  their  effect— viz.,  to  excite  nerve 
activity — by  causing  greater  or  less  temporary  or  perma- 
nent changes  in  the  nerve-substance. 

Electricity  is  preferable  as  an  agent  in  the  exciting  of 
nerve  activity  for  experimental  purposes,  as  it  causes  the 
least  changes  in  the  nerve  substance. 

Mechanical  stimuli  are  such  as  a  blow,  tension,  pressure, 
puncture,  or  cutting.  The  activity  of  a  nerve  is  excited 
when  subjected  to  such  mechanical  treatment  :  this  is 
well  shown  by  the  sharp  pain  experienced  when  a  sensory 
nerve  is  suddenly  struck  a  blow,  or  when,  during  a  minor 
operation,  such  a  nerve  is  cut.  When  a  motor  nerve  is 
suddenly  subjected  to  a  blow,  puncture,  or  cutting,  a  sud- 
den contraction  of  the  muscle  supplied  by  that  nerve  will 
be  the  result.  Mechanical  influences  only  act  as  nerve 
stimulants  when  the  nerve  is  suddenly  subjected  to  them. 
On  the  other  hand,  they  may  cause  a  destruction  or  a 
diminution  of  the  irritabihty  when  the  nerve  is  subjected 


THE   GENERAL   STRUCTURE   OF   THE   NERVES.  339 

to  their  iiiflueDce  for  a  longer  time.  This  is  well  shown 
by  the  temporary  paralysis,  peculiar  sensation,  and  anaes- 
thesia of  a  part  experienced  in  the  condition  commonly 
known  as  the  "  falling  asleep  "  of  a  limb.  The  condition 
is  produced  by  pressure  of  the  motor  and  sensory  nerves  of 
that  limb. 

That  continued  pressure  totally  destroys  irritability  is 
shown  by  paralysis  produced  in  certain  regions  by  the 
pressure  of  tumors,  aneurisms,  crutches,  etc.,  upon  nerves. 

When  a  nerve  is  subjected  to  moderate  and  short-con- 
tinued tension  its  irritabihty  is  at  first  increased.  It  is  for 
this  reason  that  nerve-tension  is  employed  in  the  treatment 
of  certain  nervous  affections,  as  neuralgias,  etc. 

Thermal  agents — viz.,  heat  and  cold — when  suddenly  ap- 
plied, act  as  nerve-stimuli.  When  a  nerve  is  subjected  to 
their  influence  for  a  longer  time  its  irritability  is  dimin- 
ished or  totally  and  permanently  destroyed.  Heat  at  first 
increases  and  then  quickly  destroys  nervous  irritability. 
Cold  gradually  diminishes  the  same.  This  is  well  shown 
by  the  local  anaesthesia  produced  by  subjecting  a  part  to 
the  influence  of  cold  for  a  time. 

Chemical  agents — such  as  solutions  of  mineral  and  or- 
ganic acids,  alkalies,  certain  mineral  and  metallic  salts, 
bile,  sugar,  alcohol,  ether,  and  chloroform — act  as  nerve- 
stimuli  and  also  influence  the  irritability  of  nerves. 

Electricity  applied  to  a  nerve  acts  as  a  stimulus,  excit- 
ing its  activity.  The  influence  of  an  electrical  current  as  a 
nerve-stimulant  is  produced  most  perceptibly  when  the 
strength  of  the  electrical  current  is  suddenly  altered  or 
when  it  is  frequently  interrupted. 

Fatigue  ain.di  prostration  of  a  nerve,  as  shown  by  a  dimin- 
ished activity,  are  produced  by  over-stimulation  and  by 
long-continued  activity  with  insufficient  periods  of  rest. 
Fatigue  of  a  nerve  is,  like  that  of  a  muscle,  due  to  an  ac- 
cumulation of  the  products  of  retrogressive  metamorphosis. 
It  has  been  observed  that  nerve  fatigue  is  produced  more 


330     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

slowly  than  muscular  fatigue.  Total  inactivity  of  a  nerve 
also  diminishes,  and  finally  destroys,  its  irritability,  as 
shown  by  degeneration  in  paralytic  conditions.  Certain 
drugs,  such  as  veratrine,  strychnine,  etc.,  influence  ner- 
vous irritability.  They  at  first  increase,  and  after  a  long- 
continued  use,  diminish,  irritability. 

2.  The  Natural  Inherent  Electrical  Currents  in  Nerves. 
— Du  Bois-Reymond  has  demonstrated  that  in  nerves,  as 
in  muscles  and  other  structures  of  the  animal  body,  there 
exist  natural  inherent  electrical  currents.  To  demonstrate 
the  presence  of  these  the  same  apparatus  is  used  as  is  em- 
ployed to  demonstrate  the  natural  electrical  currents  in 
muscle  tissue — viz. ,  a  pair  of  unpolarized  electrodes  and  a 
galvanometer. 

Not  having  the  time  to  dwell  in  detail  on  the  subject  of 
electro-physiology,  I  will  only  say  that  in  general  the  rules 
and  laws  governing  the  natural  electrical  currents  in 
muscle,  and  the  changes  taking  place  in  the  electrical  con- 
dition of  a  muscle  during  its  activity,  as  I  have  briefly 
explained  them  in  my  lectures  on  muscular  motion,  also 
apply  to  the  electrical  condition  of  nerves. 

The  Chemical  Composition  and  ProjMrties  of 
Nerve- Substance. 

Nerve-tissue  is  composed  of  (a)  water,  (6)  albuminous 
substances,  (c)  albuminoid  substances,  (d)  substances  re- 
sembling fat,  (e)  waste  products,  and  (/)  inorganic  salts. 

(a)  Waaler. — Gray  norve-substance  contains  53  to  8-i  per 
cent,  the  white  substance  60  to  TO  per  cent,  of  water. 

(b)  The  album  1710218  materials  of  the  nerve-tissue  are 
contained  principally  in  the  protoplasm  of  the  nerve-  or 
ganglion-cells  and  in  the  axis-cylinder.  The  exact  nature 
of  these  albumins  is  not  known  ;  one  of  them  resembles 
the  myosin  of  the  muscles. 

(c)  The  albuminoid  ingredients  of  nerve-tissue  are  : 

1.  Neurokeratin.     This  is  a   substance   which   contains 


THE  GENERAL   STRUCTURE   OF   THE   NERVES.  331 

no    phosphorus  but   is    rich   in    sulphur;  it   is   contained 
largely  in  the  neuroglia. 

2.  A  substance  resembling  elastin  is  derived  from  the 
myeline  sheath. 

3.  Gelatin,  derived  from  the  connective  tissue  of  the 
nerves. 

{d)  Substances  which  resemble  fats  and  are  soluble  in 
ether.     These  are  : 

1.  Protagon,  constituting  the  principal  ingredient  of  the 
brain  substance.  It  contains  N,  S,  and  P:  it  is  not  con- 
tained in  nerve-  or  ganglion-cells. 

2.  Lecithin,  a  substance  which  is  combined  with  pro- 
tagon. 

3.  Cerehrin  is  considered  a  decomposition  product  of 
protagon;  it  does  not  contain  P. 

4.  Cholesterin,  a  hydrocarbonaceous  substance. 

5.  Oleophosphoric  acid,  a  decomposition  product  of  leci- 
thin. 

(e)  Products  of  the  retrogressive  metamorphosis  or  dis- 
similation of  the  nerve-substances.     These  are  : 

1.  Xanthin. 

2.  Hypoxanthin, 

3.  Kreatin. 

4.  Urea. 

5.  Uric  acid. 

6.  Aniidic  acid. 

7.  Acetic  acid. 

8.  Inosit. 

9.  Taurin. 

10.  Lactic  acid. 

(/)  Inorganic  salts.  These  are  principally  the  chlorides 
and  phosphates  of  sodium,  potassium,  magnesium,  and 
calcium. 

The  reaction  of  nerve-tissue  in  a  fresh  state  is  alkaline, 
but  it  becomes  acid  soon  after  death,  which  is  believed  to 
be  due  to  the  formation  of  lactic  acid. 


332     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  reaction  of  nerve-fibres  varies  in  different  conditions. 
It  is,  like  that  of  the  muscular  fibres,  alkaline  or  neutral 
in  the  resting  condition,  and  acid  in  the  active  condition. 

After  death  nerve-tissue  becomes  and  remains  for  a 
time  firm  and  stiff,  which  is  believed  to  be  due  to  pro- 
cesses analogous  to  those  taking  place  in  muscle-tissue  in 
rigor. 

The  Nutrition  and  the  Metabolism  of  Nerve- Tissue. 

The  particles  of  nerve-tissue  derive  the  materials  for 
their  nutrition  from  the  parenchymatous  fluid  in  the  tissue, 
which  is  supplied  by  the  blood. 

Exactly  which  materials  are  assimilated  is  not  known. 
It  is  believed  that  the  metabolic  processes  in  the  nerve- 
tissue  are  much  less  active  than  in  any  other,  but  the 
abundaiit  vascular  supply  to  the  nerve  structures,  espe- 
cially to  the  great  centres,  and  the  occurrence  of  the 
various  products  of  retrogressive  metamorphosis,  show  the 
presence  of  metabolic  processes.  The  importance  of  these 
processes  is  also  well  demonstrated  by  the  disturbances 
produced  when  the  vascular  supply  is  interfered  with. 

The  exchange  of  the  gases  C0„  and  0  has  not  been 
demonstrated,  but  the  immediate  effect  produced  on  the 
activity  of  nerve  structures  when  the  normal  exchange  of 
these  gases  is  disturbed  in  the  system,  clearly  shows  that 
this  process  is  as  important  for  the  normal  activity  of 
nerve -tissue  as  for  any  other  structure.  It  is  probable 
that  the  exchange  of  these  gases  is  less  active  than  in 
other  tissues. 

The  nutrition  and  also  the  growth  and  development  of 
nerves  is  governed  by  special  centres,  which  are  called  the 
trophic  centres.  The  nerve-centre  from  which  a  nerve 
arises  is  generally  its  trophic  centre.  When  through  in- 
jury or  disease  a  nerve  is  severed  from  its  connection  with 
its  trophic  centre,  then  the  distal  end  undergoes  degene- 
ration. 


THE  GENERAL  STRUCTURE  OF  THE  NERVES.      333 

A  regeneration  of  nerve- substance  by  which  the  cut 
ends  of  a  nerve  reunite,  the  distal  end  gradually  regaining 
its  functions  and  properties,  takes  place  under  certain 
circumstances. 

The  process  of  regeneration  always  begins  in  the  central 
part  of  the  cut  nerve. 

Nerve- suture,  as  practised  in  surgery,  is  based  upon  this 
regenerative  power. 


LECTURE  XXXVI. 

THE  CENTRAL  ORGANS  OF  THE  CEREBROSPINAL  NERVOUS 
SYSTEM,  THEIR  STRUCTURE  AND  FUNCTIONS. 

The  central  organs  of  the  cerebro-spinal  nervous  system 
are  the  brain  and  the  spinal  cord. 

To  understand  their  physiology  it  is  necessary  to  be 
familiar  with  their  minute  anatomy. 

The  Brain. 

The  brain  is  that  portion  of  the  cerebro-spinal  axis  con- 
tained in  the  cranial  cavity.  The  different  structures 
composing  the  brain  are  covered  by  three  membranes, 
called  the  dura  mater,  the  arachnoid,  and  the  pia  mater. 

The  dura  mater  is  a  tough,  dense,  fibrous  membrane. 
It  forms  the  outer  covering  of  the  brain,  and  is  adherent 
to  the  inner  surface  of  the  cranial  bones,  forming  their 
periosteum. 

The  inner  surface  of  the  dura  mater  is  lined  with  flat 
endothelial  cells. 

The  arachnoid  forms  the  middle  covering  of  the  brain. 
It  is  a  delicate  membrane  composed  of  fibrous  and  areolar 
tissue;  its  outer  surface  is  covered  with  flat  epithelial  cells. 
The  space  between  the  under  surface  of  the  dura  mater 
and  the  outer  surface  of  the  arachnoid  is  called  the  sub- 
dural space;  this  is  a  serous  cavity  and  contains  serous 
fluid. 

The  pia  mater  is  a  delicate  vascular  membrane  which  is 
closely  adherent  to  the  outer  surface  of  the  brain  and  sends 
prolongations  into  the  fissures  on  its  surface.  The  pia 
mater  also  sends  a  prolongation,  known  as  the  velum  inter- 


THE  BRAIN — THE   CEREBRUM.  335 

positum,  into  the  interior  of  the  general  ventricular  cavity 
of  the  cerebrum  through  its  transverse  fissure. 

The  outer  surface  of  the  pia  mater  is  connected  by 
fibrous  trabeculse  with  the  arachnoid.  The  space  between 
these  two  membranes  is  called  the  subarachnoidian  space, 
and  also  contains  serous  fluid. 

The  dura  mater  sends  three  prolongations  into  the  cranial 
cavity,  which  pass  between  the  various  structures  of  the 
brain.  These  processes  are  the  falx  cerebri,  the  falx  cere- 
belli,  and  the  tentorium  cerebelli. 

The  falx  cerebri  passes  into  the  longitudinal  fissure  be- 
tween the  two  cerebral  hemispheres. 

The/aZa?  cerebelli  passes  into  the  fissure  between  the  two 
cerebellar  hemispheres. 

The  tentorium  cerebelli  passes  between  the  under  surface 
of  the  occipital  lobes  of  the  cerebrum  and  the  upper  surface 
of  the  cerebellum. 

The  function  of  the  membranes  of  the  brain  is  to  protect 
it.  The  presence  of  serous  fluid  in  the  subdural  and  the 
subarachnoidian  space  protects  the  brain  from  the  effects 
of  concussion  or  external  violence.  The  pia  mater  serves 
to  support  blood-vessels  for  the  supply  of  the  brain. 

The  iveight  of  the  brain  divested  of  its  membranes  is  49 
ounces  or  1,570  grammes  in  the  male,  and  44  ounces  or 
1,420  grammes  in  the  female.  These  weights  are  not  the 
absolute,  but  average  weights. 

The  various  parts  composing  the  brain  are:  the  cere- 
brum, the  cerebellum,  the  pons  Varolii,  and  the  medulla 

oblongata. 

The  Cerebrum. 

The  cerebrum  is  the  largest  portion  of  the  brain.  It  oc- 
cupies the  whole  anterior  and  middle,  and  a  large  portion  of 
the  posterior,  part  of  the  cranial  cavity. 

The  cerebrum  presents  for  examination  an  outer,  ex- 
terior, or  upper  surface,  an  under  surface  or  base,  and  its 
interior. 


336     LECTURES   ON   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

Tlie  Outer,  Exterior,  or  Upper  Surface  of  the  Cerebrum. 
— This  surface  is  directed  toward  the  concave  roof  of  the 
cranial  cavity  ;  it  is  convex  from  side  to  side  and  from 
the  front  backward.  The  outKne  of  the  circumference  of 
the  cerebrum  is  oval,  being  longer  in  the  antero  posterior 
than  in  the  lateral  diameter,  and  somewhat  narrower  in 
front  than  behind. 

The  cerebrum  is  divided  by  a  fissure,  called  the  longitudi- 
nal fissure,  into  halves  called  the  hemisphei^es. 

The  great  longitudinal  fissure  passes  from  the  front  back- 
ward along  the  middle  line  of  the  cerebrum.  On  the  up- 
per surface  this  fissure  separates  the  two  hemispheres  com- 
pletely. On  the  under  surface,  or  base,  this  fissure  only 
separates  the  hemispheres  completely  anteriorly  and  pos- 
teriorly, while  in  the  middle  they  are  connected  by  a  trans- 
verse band  of  white  nerve-substance  called  the  great  trans- 
verse commissure  or  the  corpus  callosum  of  the  cerebrum. 
The  upper  surface  of  this  is  seen  in  the  bottom  of  the  supe- 
rior longitudinal  fissure  when  the  hemispheres  are  held 
apart. 

Each  cerebral  heinisphere  presents  for  examination  an 
outer,  an  under,  and  an  internal  surface. 

The  outer  surface  forms  one  lateral  half  of  the  outer  sur- 
face of  the  whole  cerebrum.  It  is  convex  from  the  front 
backward  and  from  side  to  side;  it  is  directed  toward  the 
concave  interior  of  one-half  of  the  roof  of  the  cranial 
cavity. 

The  under  surface  forms  one  lateral  half  of  the  base  of 
the  cerebrum.  It  is  irregular  in  form  and  rests  anteriorly 
in  the  anterior  fossa  of  the  cranial  cavity,  with  its  middle 
portion  in  the  middle  fossa,  and  with  its  posterior  portion 
on  the  upper  surface  of  the  cerebellum  on  its  respective 
side. 

The  inner  surface  is  flat.  It  is  directed  toward  the  inner 
surface  of  the  cerebral  hemisphere,  on  the  other  side,  and 
forms  the  lateral  wall  of  the  longitudinal  fissure. 


THE   CEREBRUM.  337 

These  surfaces  of  the  cerebral  hemispheres  present  vari- 
ous longitudinal  furrows  of  a  greater  or  less  depth.  They 
pass  in  an  apparently  irregular  course  in  different  direc- 
tions on  the  surfaces  of  the  cerebral  hemispheres,  giving 
them  a  lobulated  and  convoluted  appearance.  These  fur- 
rows are  divided  into  fissures  and  sulci. 

The  fissures  are  deep  furrows  which  penetrate  into  the  sub- 
stance of  the  cerebral  hemispheres,  dividing  it  into  portions 
called  the  lobes.  The  fissures  are  formed  during  the  de- 
velopment of  the  cerebrum,  by  an  involution  of  its  mass.    ' 

They  are  constant  and  are  the  same,  as  regards  their 
position,  course,  and  arrangement,  in  all  brains  of  the  same 
species. 

The  cerebral  hemispheres  of  the  human  brain  present 
three  fissures — namely,  the  fissure  of  Rolando,  the  fissure 
of  Sylvius,  and  the  occipito-parietal  fissure. 

The  fissure  of  Rolando  begins  at  the  tipper  border  of  the 
superior  longitudinal  fissure,  at  about  its  centre  ;  it  then 
passes  downward  and  slightly  forward  on  the  outer  sur- 
face of  the  cerebral  hemisphere,  terminating  a  little  above 
the  horizontal  limb  of  the  fissure  of  Sylvius  and  a  little 
behind  the  ascending  limb  of  the  same  fissure.  The  fissure 
of  Rolando  divides  the  cerebral  hemisphere  on  its  outer 
surface  into  tw^o  lobes — one  anterior  to  the  fissure,  called 
the  frontal  lobe,  and  one  posterior  to  the  fissure.  This 
part  is  again  divided  into  lobes  by  other  fissures.  That 
portion  directly  behind  the  fissure  of  Rolando  is  termed 
the  parietal  lobe. 

The  occipito-parietal  fissure  begins  at  the  lower  border 
of  the  longitudinal  fissure  posteriorly,  then  passes  upward 
along  the  inner  surface  of  the  cerebral  hemisphere,  and 
then  downward  and  forward  for  about  an  inch  on  the 
outer  surface. 

This  fissure  separates,  on  the  inner  and  outer  surface,  a 
portion  from  the  parietal  lobe;  this  posterior  portion  is 
called  the  occipital  lobe. 

22 


338      LECTURES   OX   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  fissure  of  Sylvius  begins  at  the  under  surface  of  the 
cerebral  hemisphere,  near  the  centre.  From  there  the 
fissure  passes  outward  toward  the  outer  borders,  and, 
winding  around  this  to  the  outer  surface,  it  divides  it  into 
two.  One.  the  ascending  limb,  passes  upward  on  the  outer 
surface,  terminating  in  front  of  the  lower  end  of  the  fis- 
sure of  Rolando.  The  other,  the  horizontal  limb,  passes 
for  a  short  distance  upward  on  the  outer  surface,  and  then 
horizontally  backward,  and  separates  a  portion  from  the 
lower  part  of  the  parietal  lobe:  this  is  called  the  temporo- 
■sphenoidal  lobe. 

These  three  fissures — viz.,  the  fissure  of  Rolando,  the 
occipito-parietal  fissure,  and  the  fissure  of  Sylvius — divide 
'each  cerebral  hemisphere  into  four  lobes,  called  the  fron- 
tal, parietal,  occipital,  and  temporo-sphenoidal  lobe. 

The  frontal  lobe  is  that  portion  which  is  situated  in 
front  of  the  fissure  of  Rolando. 

The  parietal  lobe  is  the  portion  behind  the  fissure  of 
Rolando,  in  front  of  the  occipito-parietal  fissure,  and  above 
the  horizontal  limb  of  the  fissure  of  Sylvius. 

The  occipital  lobe  is  the  portion  posterior  to  the  occipito- 
parietal fissure. 

The  temporo-splienoidal  lobe  is  the  portion  beneath  the 
horizontal  limb  of  the  fissure  of  Sylvius. 

On  the  Older  surface  of  the  cerebral  hemisphere  are  seen 
the  outer  surfaces  of  the  frontal,  the  parietal,  the  occipital, 
and  the  tempore  sphenoidal  lobes. 

On  the  inner  surface  of  the  cerebral  hemisphere  are  seen 
the  inner  surfaces  of  the  frontal,  the  parietal,  and  of  the 
occipital  lobe. 

On  the  under  surface  of  the  cerebral  hemisphere  are 
seen  :  (1)  The  under  surface  of  the  frontal  lobe— viz.,  that 
portion  of  the  under  surface  of  the  hemisphere  which  is 
anterior  to  the  fissure  of  Sylvius — this  is  also  called  the 
anterior  lobe;  (2)  the  under  surface  of  the  temporo-sphe- 
noidal lobe—  this  is  also  called  the  middle  lobe  :  and  (3)  the 


THE   CEREBRUM.  339 

under  surface  of  the  occipital  lobe — viz.,  that  portion  of 
the  under  surface  of  the  hemisphere  which  is  in  contact 
with  a  lateral  half  of  the  upper  surface  of  the  cerebellum 
(this  is  also  called  the  x>osterior  lobe). 

In  the  fissure  of  Sylvius,  at  the  base  of  the  hemisphere, 
there  is  a  fifth  lobe,  called  the  central  lobe,  or  the  island  of 
Reil.  This  is  visible  only  when  the  fissure  of  Sylvius  is 
held  apart  at  the  base. 

The  island  of  Reil  is  a  triangular-shaped  mass  which  is 
separated  from  the  frontal,  parietal,  and  the  temporo- 
sphenoidal  lobes  by  three  short,  deep  fissures  or  sulci, 
called  the  anterior,  external,  and  posterior  sulcus  of  Reil. 

The  anterior  sulcus  of  Reil  separates  the  island  of  Reil 
from  the  posterior  orbital  convolution,  from  the  anterior 
lobe,  or  the  under  surface  of  the  frontal  lobe  in  front. 

The  external  sulcus  of  Bell  separates  the  island  of  Reil 
from  the  inferior  part  of  the  inferior  frontal,  the  ascending 
frontal,  and  the  ascending  parietal  convolution. 

The  posterior  sulcus  ov  fissure  of  Reil  separates  the  island 
of  Reil  from  the  temporo- sphenoidal  lobe  which  is  poste- 
rior to  this  sulcus. 

The  sulci  are  shallow,  longitudinal  furrows  which  pass 
over  the  surfaces  of  the  cerebral  lobes  in  various  directions 
and  branch  in  their  course,  and  which  give  to  the  sur- 
faces of  the  cerebral  lobes  a  convoluted  appearance.  The 
sulci  are  not  constant  anatomical  points.  They  are  not 
equally  present,  and  not  equally  developed,  as  regards  their 
course,  depth,  and  general  arrangement,  in  all  brains  of  one 
species.  The  sulci  develop  and  become  more  marked  as 
the  intelligence  and  psychical  functions  of  the  individual 
develop. 

The  exterior  of  the  cerebral  hemispheres  consists  of  a 
layer  of  gray  nerve-substance,  which  is  called  the  cortex  of 
the  hemisphere,  in  contradistinction  to  its  interior  white 
nerve-substance  which  is  called  the  medullary  portion. 

The  cortical  gray  substance  of  the  cerebral  hemispheres 


340     LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

is  regarded  as  the  seat  of  intelligence  and  the  higher 
psychical  functions,  and  the  purpose  of  the  sulci  and 
fissures  is  to  increase  the  surface  for  the  development 
of  the  cortical  gray  substance  without  an  increase  of  the 
surface  of  the  cerebrum  itself.  The  cortical  gray  substance 
also  covers  the  sides  and  floor  of  the  sulci,  and  the  surface 
is  therefore  greater  when  the  sulci  are  well  marked,  deep, 
and  long  than  when  they  are  not  well  developed.  It  is,, 
for  instance,  well  known  that  the  sulci  on  the  cerebral  sur- 
face of  the  brains  of  cretins  and  idiots  are  not  well  devel- 
oped.   This  is  the  case  in  animals,  apes,  dogs,  etc. 

The  protruding  convex  masses  between  the  sulci  are 
called  the  convolutions. 

I  will  describe  only  some  of  the  more  prominent  and  con- 
stant sulci  and  convolutions  of  the  cerebral  lobes,  a  know- 
ledge of  which  is  essential,  as  they  are  anatomical  points 
important  in  the  localization  of  the  seats  of  the  various- 
functions. 

The  more  prominent  sulci  and  convolutions  on  the  sur- 
face of  the  cerebral  hemispheres  are: 

(a)  Those  of  the  Frontal  Lobe. — The  outer  surface  of  the 
frontal  lobe  presents  three  sulci— viz.,  the  pre-central  sul- 
cus, which  runs  parallel  with,  and  a  little  in  front  of,  the 
fissure  of  Rolando  ;  and  the  superior  and  inferior  frontal 
sulci,  which  divide  the  portion  in  front  of  the  pre-central 
sulcus  into  three  horizontal  convolutions,  named  respec- 
tively the  superior,  middle,  and  inferior  frontal  convolution. 

The  superior  frontal  convolution  is  that  portion  of  the 
outer  surface  of  the  frontal  lobe  which  is  situated  above  the 
superior  frontal  sulcus  and  in  front  of  the  pre-central  sulcus. 

The  middle  frontal  convolution  is  that  portion  which  is 
situated  between  the  superior  and  inferior  frontal  sulci 
and  in  front  of  the  pre-central  sulcus. 

The  inferior  frontal  convolution  is  that  portion  of  the 
frontal  lobe  which  is  situated  beneath  the  inferior  frontal 
sulcus  and  in  front  of  the  pre-central  sulcus. 


THE    CEREBRUM.  341 

That  portion  of  the  frontal  lobe  which  is  situated  behind 
iihe  pre- central  sulcus  and  in  front  of  the  fissure  of  Eo- 
lando  is  called  the  ascending  frontal  convolution. 

The  inferior  surface  of  the  frontal  lobe  is  that  portion  of 
"the  base  of  the  cerebral  hemisphere  which  is  situated  an- 
teriorly to  the  fissure  of  Sylvius;  this  portion  is  also  called 
the  orbital  or  the  anterior  lobe.  It  rests  upon  the  orbital 
plate  of  the  frontal  bone. 

This  surface  presents  two  sulci — viz  ,  the  orbital  and  the 
olfactory  sulci. 

The  olfactori/  sulcus  or  fissure  is  a  deep  furrow  which 
l)egins  in  front  of  the  optic  comniissure  and  passes  forward 
to  nearly  the  anterior  border  of  the  froutal  lobe,  parallel 
wuth  and  a  Uttle  external  to  the  anterior  portion  of  the 
longitudinal  fissure.  The  narrow  convolution  internal  to 
this  sulcus  is  the  under  margia  of  the  marginal  convolution 
of  the  internal  surface  of  the  hemisphere. 

The  portion  of  the  orbital  lobe  external  to  the  olfactory 
sulcus  is  divided  by  the  oj)tic  sulcus,  which  passes  trans- 
versely and  has  several  rami,  or  minor  sulci,  passing  from 
it  in  various  directions. 

The  three  lobes  into  which  this  portion  is  thus  divided 
are  called  respectively  the  internal,  the  anterior,  and  the 
jDOsterior  orbital  convolutions. 

That  portion  of  the  cerebral  hemisphere  which  forms  the 
Toof  of  the  fissure  of  Sylvius  is  composed  of  the  inferior 
part  of  a  small  portion  of  the  inferior  frontal  convolu- 
tion, of  the  lower  portions  of  the  ascending  frontal  and  of 
the  ascending  parietal  convolution,  and  of  the  triangular 
mass  known  as  the  island  of  Eeil. 

The  surface  which  is  made  up  of  the  convolutions  just 
mentioned  presents  three  marked,  distinct,  and  several 
minor  sulci.  The  three  marked  sulci  are  the  anterior,  the 
posterior,  and  the  external  sulcus  of  Reil. 

The  anterior  sulcus  or  fissure  of  Reil  separates  the  pos- 
terior orbital  convolution  from  the  island  of  Reil. 


342     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  external  sulcus  or  fissure  of  Reil  separates  the  under 
portion  of  the  inferior  orbital,  the  ascending  frontal,  and 
the  ascending  parietal  convolution  from  the  island  of  Reil. 

The  jjosterior  sulcus  of  Reil  separates  the  island  of  Reil 
from  the  mass  of  the  temporo-sphenoidal  lobe. 

The  surface  of  the  island  of  Reil  is  divided  by  minor  sulci 
into  several  lobes  or  convolutions,  which  are  called  gyri 
operti. 

(b)  The  Sulci  and  Convolutions  of  the  Parietal  Lobe. 
— The  surface  of  the  parietal  lobe  has  two  sulci — viz.,  the 
intraparietal  and  the  post -central  sulcus. 

The  intrajKirietal  sulcus  begins  a  little  posteriorly  to  the 
lower  end  of  the  fissure  of  Rolando.  It  then  ascends  ver- 
tically for  a  short  distance,  and  finally  curves  backward,, 
terminating  at  the  border  of  the  longitudinal  fissure  a  little 
in  front  of  the  external  occipito-parietal  fissure. 

The  post-central  sulcus  is  continuous  with  the  ascending 
portion  of  the  intraparietal,  and  ascends  from  it  to  the 
border  of  the  longitudinal  fissure,  running  parallel  with 
and  a  little  posteriorly  to  the  upper  part  of  the  fissure  of 
Rolando. 

These  two  sulci  divide  the  outer  surface  of  the  parietal 
lobe  into  three  convolutions— viz.,  the  ascending,  the  supe- 
rior, and  the  inferior  parietal  convolutions. 

The  ascending  jparietcd  convolution  is  that  portion  which 
is  situated  in  front  of  the  ascending  part  of  the  intra- 
parietal sulcus  and  the  post-central  sulcus  and  behind  the 
fissure  of  Rolando. 

The  superior  parietal  convolution  is  the  portion  above 
the  covered  part  of  the  intraparietal  sulcus  and  behind  the 
post-central  sulcus. 

The  inferior  parietal  convolution  consists  of  two  por- 
tions— an  anterior  w^hich  is  called  the  supramarginal  por- 
tion, and  a  posterior  which  is  called  the  angidar  portion  j 
the  two  are  divided  by  a  shallow  sulcus.  The  supramargi- 
nal portion  is  bounded  in  front  by  the  lower  part  of  the 


THE   CEREBRUM.  343 

fissure  of  Rolando,  being  connected  here  with  the  ascending 
parietal  convolution;  below,  it  is  bounded  by  the  horizontal 
limb  of  the  fissure  of  Sylvius;  above,  by  the  intraparietal 
sulcus;  and  anteriorly  it  is  continuous  with  the  angular 
portion. 

The  angular  portion  is  connected  in  front  with  the  supra- 
marginal  portion;  above,  it  is  bounded  by  the  intraparietal 
sulcus;  behind,  it  is  connected  with  the  second  annectant 
gyrus,  which  is  a  portion  of  the  middle  occipital  convolu- 
tion ;  below,  it  is  connected  with  the  middle  temporo- 
sphenoidal  convolution. 

(c)  The  Sulci  and  Convolutions  of  the  Occijyital  Lobe. — 
The  outer  surface  of  the  occipital  lobe  is  divided  by  two 
indistinctly  marked  sulci  into  three  convolutions.  The 
sulci  are  the  superior  and  middle  occipital  sulci. 

The  superior  occipital  sulcus  curves  upward  along  the 
posterior  part  of  the  lobe  ;  it  is  continuous  above  with  the 
backward-curving  portion  of  the  intraparietal  sulcus  ;  be- 
low, it  joins  the  horizontally  running  middle  occipital 
sulcus. 

The  middle  occipital  sulcus  begins  at  the  inferior  border 
of  the  occipital  lobe,  and  then  passes  obliquely  upward  and 
backward,  joining  the  superior  occipital  sulcus. 

The  occipital  lobe  is  divided  by  these  two  sulci  into  three 
convolutions,  named  respectively  the  superior,  the  middle, 
and  the  inferior  occipital  convolutions. 

The  superior  occijyital  convolution  is  the  portion  above 
the  superior  occipital  sulcus.  This  portion  is  connected 
with  the  superior  parietal  convolution  by  a  process  which 
is  called  the  first  annectant  gyrus. 

The  middle  occipital  convolution  is  the  portion  between 
the  superior  and  middle  occipital  sulci.  This  portion  is 
connected  in  front  and  above  with  the  angular  portion  of 
the  inferior  parietal  convolution  by  a  process  which  is 
called  the  second  annectant  gyrus.  Below  and  in  front 
the  middle  occipital  convolution  is  connected   with  the 


344     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

middle  temporo-sphenoidal  convolution  by  another  process, 
which  is  called  the  third  annectant  gyrus. 

The  inferior  occipitpJ  convolution  is  the  portion  below 
the  middle  occipital  sulcus.  This  portion  is  connected 
in  front  with  the  inferior  temporo-sphenoidal  convolution 
by  a  process  called  the  fourth  annectant  gyrus. 

(d)  The  Sulci  and  Conr  olid  ions  of  the  TemjDoro-Sphenoidcd 
Lobe. — The  surface  of  the  temporo-sphenoidal  lobe  is  divided 
by  two  sulci  into  three  convolutions.  The  sulci  are  the 
superior  and  inferior  temporo-sphenoidal  fissure  or  sul- 
cus. 

The  superior  temporo-sjyhenoidal  sulcus  runs  a  little  be- 
low and  parallel  with  the  horizontal  limb  of  the  fissure  of 
Sylvius. 

The  inferior  temporo-sphenoidcd  sulcus  runs  a  little  be- 
low and  parallel  with  the  former.  These  two  sulci  divide 
the  outer  surface  of  the  temporo-sphenoidal  lobe  into  three 
convolutions,  called  the  superior,  middle,  and  inferior  tem- 
poro-sphenoidal convolutions. 

The  superior  temporo  sphenoidal  convolution  is  the  por- 
tion between  the  horizontal  limb  of  the  fissure  of  Sylvius 
and  the  superior  temporo-sphenoidal  sulcus.  Posteriorly 
this  convolution  is  connected  with  the  supramarginal  por- 
tion of  the  inferior  parietal  convolution. 

The  middle  temporo-sphenoidal  convolution  is  the  por- 
tion between  the  superioi'  and  inferior  temporo-sphenoidal 
sulci.  This  convolution  is  connected  behind  with  the  an- 
gular portion  and  with  the  third  annectant  gyrus  of  the 
middle  occipital  convolution. 

The  inferior  temporo-sphenoidal  convolution  is  the  por- 
tion below  the  inferior  temporo-sphenoidal  sulcus.  This 
portion  is  connected  behind  with  the  fourth  annectant 
gyrus  of  the  inferior  occipital  convolution. 

The  inner  surface  of  the  cerebral  hemisphere  is  also 
divided  by  sulci  into  convolutions. 

This  surface  presents   five  well-marked  fissures — viz., 


THE  CEREBRUM.  345 

the  calloso-niarginal,    the  parieto-occipital,  the  calcarine, 
the  collateral,  and  the  dentate. 

The  calloso-marginal  fissure  begins  beneath  the  curved 
anterior  end  of  the  corpus  callosum  ;  it  then  curves  for- 
ward and  upward  over  the  anterior  end,  and  then  curves 
l)ackward,  and  finally  passes  upward,  terminating  at  the 
upper  border  of  the  internal  surface  a  little  behind  the 
beginning  of  the  fissure  of  Rolando.  In  its  course  the 
calloso-marginal  fissure  runs  parallel  with  the  curved  an- 
terior end  and  the  rostrum  or  upper  surface  of  the  corpus 
callosum,  dividing  that  portion  of  the  internal  surface  of 
the  hemisphere  which  is  located  beneath  and  in  front  of 
the  anterior  end,  and  above  the  rostrum  of  the  corpus  cal- 
losum, into  two  convolutions,  which  are  called  the  marginal 
convolution  and  the  gyrus  fornicatus,  or  the  convolution 
of  the  corpus  callosum. 

The  marginal  convolution  is  the  portion  above  or  exter- 
nal to  the  calloso-marginal  convolution.  The  surface  pre- 
sents several  minor  sulci. 

The  gyrus  fornicatus,  also  called  the  convolution  of  the 
corpus  callosum,  is  the  portion  between  the  calloso-mar- 
ginal fissure  and  the  upper  border  of  the  anterior  end  and 
upper  surface  of  the  corpus  callosum. 

The  occipito-parietal  fissure  begins  a  little  behind  and  on 
-a  level  wibh  the  splenium,  or  posterior  end  of  the  corpus 
callosum.  This  fissure  passes  from  this  point  obliquely 
backward  and  upward,  and  is  continuous  at  the  upper 
border  of  the  internal  surface  with  the  external  parieto- 
occipital fissure. 

•  That  portion  of  the  internal  surface  which  is  situated 
between  this  internal  parieto-occipital  fissure  and  the  as- 
cending part  of  the  calloso-marginal  fissure  is  called  the 
■quadrate  lobe. 

The  calcarine  fissure  begins  at  the  same  point  where  the 
internal  portion  of  the  parieto-occipital  fissure  begins.  It 
passes  from  this  point  obliquely  backward  and  downward. 


346     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  triangular  portion  of  the  internal  surface  betweert 
the  parieto-occipital  fissut-e  above  and  the  calcarine  fissure 
below  is  called  the  cmieafe  lobe. 

The  collateral  fissure  begins  beneath  the  calcarine  fissure; 
it  runs  parallel  with  the  latter  and  then  continues  forward, 
terminating  near  the  beginning  of  the  fissure  of  Sylvius. 
This  fissure  divides  that  portion  of  the  internal  surface 
which  is  located  beneath  the  calcarine  fissure  and  beneath 
the  corpus  callosum  into  two  long  convolutions,  called 
the  uncinate  or  internal  occipito-temporal  convolution, 
and  the  external  occipito-temporal  convolution. 

The  uncinate  or  internal  occipito-tenqmral  convolution 
is  the  portion  above  the  collateral  fissure.  This  convolu- 
tion is  bounded  above  by  the  calcarine  and  the  dentate 
fissures. 

The  external  occipito-temporal  convolution  is  that  part 
beneath  the  collateral  fissure.  This  convolution  is  sepa- 
rated from  the  inferior  temporo-sphenoidal  convolution  by 
the  inferior  temporo-siDhenoidal  sulcus  or  fissure. 

The  dentate  fissure  is  situated  above,  and  runs  parallel 
with,  the  anterior  portion  of  the  uncinate  convolution. 
The  fissure  begins  at  the  posterior  end  of  the  corpus  cal- 
losum and  terminates  in  front  at  the  curved  end  of  the 
uncinate  convolution. 

The  internal  surface  is  divided,  by  the  arrangement  of 
these  five  fissures,  into  six  convolutions — namely,  the  mar- 
ginal convolution,  gyrus  fornicatus,  quadrate  lobe,  cuneate 
lobe,  uncinate  convolution,  and  external  occipito- temporal 
convolution. 


LECTUEE    XXXVII. 

THE  CEREBRUM  {continued). 

The  Under  Surface,  or  Base,  of  the  Cerebrum. 

The  base  of  the  cerebrum  presents  for  examination  the 
under  surface  of  the  cerebral  hemispheres  and  the  parts 
which  are  placed  along  the  middle  line. 

The  under  surface  of  each  cerebral  hemisphere  is  divided 
into  three  lobes — the  anterior,  middle,  and  posterior. 

The  anterior  or  orbital  lobe  is  that  part  of  the  under  sur- 
face of  the  frontal  lobe  which  is  situated  anteriorly  to  the 
fissure  of  Sylvius.  It  rests  upon  the  orbital  plate  of  the 
frontal  bone.  The  fissures,  sulci,  and  convolutions  of  this 
lobe  I  have  already  described. 

The  middle  lobe  rests  in  the  middle  fossa  of  the  cranium;. 
it  is  the  portion  posterior  to  the  fissure  of  Sylvius. 

The  posterior  lobe  of  each  cerebral  hemisphere  is  that 
part  of  the  under  surface  of  the  cerebrum  which  is  coA'ered 
by  the  cerebellum  behind  and  by  the  pons  Varolii  in  front 
of  this. 

If  the  cerebellum  and  the  pons  are  raised,  it  Avill  be  seen 
that  the  two  posterior  lobes  are  completely  separated  pos- 
teriorly by  the  longitudinal  fissure,  while  anteriorly  a  por- 
tion of  the  under  surface  of  the  posterior  end  or  splenium 
of  the  corpus  callosum  is  seen  between  the  two  lobes.  The 
parts  which  are  arranged  along  the  middle  line  between 
the  two  hemispheres  are: 

1.  The  crura  cerebri. 

2.  The  optic  tracts  and  the  optic  commissure. 

3.  The  parts  filling  the  interpeduncular  space. 

4.  The  anterior  perforated  space. 

5.  The  olfactory  tracts  and  their  bulbs. 


348     LECTURES   ON    HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

1.  The  C7mra  cerebri  are  two  broad  bands  which  emerge 
from  the  anterior  border  of  the  pons  Varohi  and  diverge, 
passing  forward  and  outward,  and  then  enter  the  substance 
of  the  middle  lobes  of  the  cerebral  hemisphere.  Each  crus 
consists  of  an  upper  layer  of  longitudinal  fibres,  which  is 
called  the  tegmentum;  its  fibres  are  sensory,  continuous 
with  the  longitudinal  fibres  of  the  pons.  Beneath  this 
there  is  a  layer  of  gray  nerve-substance  which  is  called  the 
locus  niger.  Again  beneath  this  is  a  third  layer,  called  the 
crusta;  it  is  the  inferior  layer  and  is  composed  of  longitudi- 
nal fibres  which  are  continuous  with  the  longitudinal  fibres 
of  the  pons;  they  are  motor  fibres. 

From  a  groove  on  the  inner  border  of  the  crura  cerebri, 
near  the  anterior  border  of  the  pons,  emerge  the  fourth 
pair  of  cranial  nerves.  From  a  groove  on  the  outer  border 
of  the  crura,  near  the  anterior  border  of  the  pons,  emerge 
the  third  pair  of  cranial  nerves. 

2.  The  optic  tracts  are  two  white,  fiattened  bands  which 
emerge  from  beneath  the  outer  border  of  the  crura  cerebri 
a  little  anteriorly  to  the  third  cranial  nerves.  These  bands 
wind  around  the  outer  border  and  then  cross  obliquely  the 
under  surface  of  the  crura;  they  converge  as  they  pass  for- 
ward and  inward,  and  finally  meet  anteriorly;  their  junc- 
tion is  called  the  oj^tic  commissure. 

3.  The  interpeduncular  space  is  the  lozenge-shaped  space 
bounded  by  the  anterior  border  of  the  pons  and  the  inner 
borders  of  the  diverging  crura  cerebri  behind,  and  by  the 
optic  commissure  and  the  converging  optic  tracts  in  front. 

This  space  is  filled  with  certain  structures,  which,  be- 
ginning posteriorly,  are  as  follows: 

The  posterior  perforated  space. 
The  corpora  albicantia. 
The  tuber  cinereum. 
The  infundibulum. 
The  pituitary  body. 
The  lamina  cinerea. 


THE  CEREBRUM.  349' 

The  posterior  perforated  space  is  a  small  mass  of  gray 
substance  placed  immediately  in  front  of  the  anterior  bor- 
der of  the  pons  between  the  diverging  crura.  This  mass  is 
perforated  by  minute  openings  for  the  transmission  of  small, 
straight  vessels. 

The  upper  surface  of  this  mass  forms  part  of  the  floor  of 
the  third  ventricle. 

The  corpora  alhicantia  are  two  small,  rounded  bodies. 
They  are  placed  side  by  side  in  front  of  the  posterior  perfo- 
rated space,  and  are  connected  by  a  commissure.  They 
consist  of  gray  nerve-substance  internally  and  white  matter 
externally. 

The  tuber  cinereum  is  a  mass  of  gray  substance  placed  in 
front  of  the  corpora  albicantia  and  behind  the  optic  com- 
missure; its  upper  surface  forms  a  part  of  the  floor  of  the 
third  ventricle. 

The  infunclibulum  is  a  small  tubular  process  from  the  in- 
ferior surface  of  the  tuber  cinereum;  attached  to  this  is  the 
pituitary  body,  a  small  glandular  organ  which  rests  in  the 
sella  turcica;  it  communicates  through  the  infundibulum 
with  the  third  ventricle. 

The  lamina  cinerea  is  a  mass  of  gray  nerve-substance 
placed  in  front  of  the  tuber  cinereum  and  above  the  optic 
commissure;  laterally  it  communicates  with  the  anterior 
perforated  space  on  each  side. 

4.  The  anterior  j)erforatecl  space  is  a  small,  perforated 
mass  of  gray  nerve-substance  which  corresponds  to  a  small 
portion  of  the  under  surface  of  the  corpus  striatum.  It  is- 
seen  on  either  side  of  the  optic  commissure,  filling  the  small 
triangular  space  which  is  bounded  internally  and  behind 
by  the  optic  commissure  and  optic  tract,  externally  by  the 
border  of  the  middle  lobe,  and  anteriorly  by  the  optic  lobe. 

5.  The  olfactory  tracts  and  their  bulbs.  The  olfactory 
tracts  are  two  bands  of  white  nerve-substance;  they  arise 
from  three  roots  in  the  anterior  perforated  space  on  each 
side,   and  pass  forward  along  the  under  surface  of  the 


350     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

frontal  lobe,  parallel  with  and  near  the  longitudinal  fis- 
sure. 

Near  the  anterior  border  of  the  frontal  lobes  the  olfac- 
tory tracts  terminate  in  bulbous  expansions  called  the  ol- 
factory bulbs,  from  which  arise  the  olfactory  nerves;  these 
enter  the  foramina  of  the  cribriform  plates  of  the  ethmoid 
bone. 

Immediately  in  front  of  the  optic  commissure  a  small 
portion  of  the  anterior  end  or  genu  of  the  corpus  callosum 
is  seen  between  the  frontal  or  anterior  lobes.  Anteriorly  to 
this  these  lobes  are  completely  separated  by  the  longitudi- 
nal fissure. 

The  Interior  of  the  Cerebrum. 

The  interior  of  each  cerebral  hemisphere  is  composed  of 
white  nerve-substance  and  of  separate  masses  of  gray  mat- 
ter; in  the  middle  the  two  cerebral  hemispheres  are  con- 
nected by  the  great  transverse  commissure  or  corpus  cal- 
losum. 

The  corpus  callosum  is  a  mass  composed  principally  of 
transverse  nerve- fibres,  which  are  placed  between  and  con- 
nect the  two  hemispheres.  It  is  about  four  inches  long, 
is  located  in  the  longitudinal  fissure,  and  extends  forward 
to  within  1^  inches  of  the  anterior  border  of  the  cerebrum 

The  corpus  callosum  is  arched  in  form.  Its  upper,  convex 
border  or  rostrum  forms  the  central  part  of  the  floor  of  the 
superior  longitudinal  fissure,  and  is  plainly  seen  when  the 
two  hemispheres  are  held  apart.  Its  lower  surface  or  bor- 
der is  concave,  is  directed  toward  the  base  of  the  cerebrum, 
and  forms  the  roof  of  the  general  ventricular  cavity. 

Anteriorly  the  corpus  callosum  terminates  in  a  round 
mass  called  the  genu;  this  arches  downward,  so  that  its 
lower  surface  is  seen  anteriorly  between  the  two  frontal 
lobes  at  the  base  of  the  cerebrum.  Posteriorly  the  corpus 
callosum  terminates  in  a  broad,  rounded  mass  called  the 
splenium;  this  arches  downward,  so  that  its  under  surface 


THE   CEREBRUM.  351 

is  seen  between  the  two  occipital  or  posterior  lobes  at  the 
T^ase  of  the  cerebrum. 

If  from  the  upper  surface  of  the  cerebrum  a  section  is 
made  above  the  upper  border  of  the  corpus  callosum,  it  will 
be  seen  that  each  cerebral  hemisphere  consists  of  an  oval 
central  mass  of  white  nerve-substance  surrounded  by  a 
margin  of  gray  matter  of  nearly  uniform  thickness. 

The  central  oval  white  mass  is  termed  the  centrum  ovale 
minus;  the  gray  margin  is  called  the  cortex.  If  from  the 
upper  surface  of  the  cerebrum  another  section  is  made 
which  includes  part  of  the  upper  border  of  the  corpus  cal- 
losum, it  wiU  be  observed  that  this  is  a  transverse  mass  of 
white  substance  which  connects  the  two  hemispheres.  The 
whole  white  central  mass  of  the  cerebrum  which  is  now 
exposed  is  called  the  centrum  ovale  majus.  If  from  the 
upper  surface  of  the  cerebrum  still  another  section  is  made 
which  includes  the  upper  portion  of  the  corpus  callosum,  a 
cavity  is  exposed  which  is  bounded  anteriorly  and  behind 
by  the  ends  of  the  corpus  callosum;  laterally  this  cavity 
extends  into  the  substance  of  the  cerebral  hemispheres, 
and  is  bounded  by  masses  of  gray  nerve  substance  which 
^re  known  as  the  large  basal  ganglia  of  the  cerebrum. 
The  floor  of  this  cavity  is  formed  by  the  structures  fiUing 
the  interpeduncular  space.  This  cavity  is  called  the  gene- 
ral ventricular  cavity  of  the  cerebrum. 

Tlie  Basal  Ganglia. 

The  various  collections  of  gray  nerve-substance  which 
are  located  along  the  middle  line  of  the  base  of  the  cere- 
brum, and  those  which  are  contained  in  the  cerebral  hemi- 
spheres near  their  inferior  surface,  are  cahed  the  hasal 
ganglia. 

These  are:  the  corpora  striata,  the  optic  thalami,  the 
corpora  quadrigemina,  and  the.  corpora  geniculata:  the 
locus  niger,  the  middle  layer  or  gray  substance  of  the  crura 
cerebri,  may  also  be  included  among  them. 


35'^     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  corpora  striata  are  masses  of  gray  nerve  substance- 
in  the  cerebral  hemispheres.  The  corpus  striatum  in  each 
cerebral  hemisphere  consists  of  two  separate  masses  called 
the  nucleus  caudatus  and  the  nucleus  lenticularis. 

The  nucleus  caudatus  is  a  pear  shaped  mass  which  is  con- 
tained in  the  hemisphere,  a  little  externally  and  below  the 
upper  part  of  the  corpus  callosum,  which  forms  the  roof 
of  the  general  ventricular  cavity. 

The  anterior  broad  extremity  is  directed  forward  and  its 
upper  surface  forms  a  part  of  the  floor  of  the  main  cavity 
of  the  lateral  ventricle.  The  posterior  tapering  end  is  di- 
rected backward  and  slightly  outward,  overlapping  the  op- 
tic thalamus,  which  is  located  posteriorly  and  a  little  inter- 
nally to  the  nucleus  caudatus. 

The  nucleus  caudatus  is  also  termed  the  intraventricular 
portion  of  the  corpus  striatum,  from  the  fact  that  it  enters 
into  the  formation  of  the  walls  of  the  general  ventricular 
cavity. 

The  nucleus  lenticularis  is  the  larger  of  the  two  portions 
of  the  corpus  striatum.  It  does  not  participate  in  the  for- 
mation of  the  walls  of  the  general  ventricular  cavity,  and 
is  therefore  termed  the  extraventricular  portion  of  the 
corpus  striatum.  This  portion  is  separated  from  the  nu- 
cleus caudatus,  w^hich  is  situated  internally  to  it,  by  a  nar- 
row bundle  of  nerve-fibres  known  as  the  internal  capsule. 

The  optic  thalami  are  two  large,  oval  masses,  one  in  each 
cerebral  hemisphere,  located  behind  aud  internally  to  the 
posterior  thin  end  of  the  nucleus  caudatus;  from  this  it  is 
separated  by  a  narrow,  rounded  band  of  nerve-fibres  called 
the  toiiiia  semicircularis. 

The  inner  surface  of  the  optic  thalamus  forms  a  part  of 
the  lateral  w^alls  of  the  third  ventricle.  Its  ujjjyer  surface 
is  directed  toward  the  floor  of  the  central  cavity  of  the 
lateral  ventricle,  and  terminates  in  front  in  a  rounded 
prominence  called  the  anterior  tubercle.  Its  under  surface 
rests  upon  the  side  of  the  tegmentum  of  the  crus  cerebri. 


THE    CEREBRUM.  353 

Its  posterior  end  is  projected  above  the  corpora  quadrige- 
mina  and  the  pineal  gland.  Projected  from  the  outer  side 
of  the  posterior  end  are  two  rounded  masses  called  the  cor- 
jpora  geniculata. 

The  corpora  quadrigemina-are  four  round  masses — an  an- 
terior pair,  called  the  nates,  and  a  posterior  pair,  called  the 
testes.  These  are  separated  on  their  superior  surface  by  a 
transverse  and  longitudinal  furrow. 

The  corpora  quadrigemina  are  situated  beneath  the  lower 
surface  of  the  posterior  end  of  the  corpus  callosum,  behind 
the  posterior  commissure  of  the  third  ventricle,  and  above 
the  upper  surface  of  the  crura  cerebri. 

Between  the  under  surface  of  the  corpora  quadrigemina 
and  the  upper  surface  of  the  crura  cerebri  there  is  a  narrow 
descending  channel  by  which  the  third  ventricle  commu- 
nicates with  the  fourth  ventricle  behind  and  below;  this 
channel  is  called  the  aqueduct  of  Sylvius.  Laterally  the 
corpora  quadrigemina  are  connected  with  the  sides  of  the 
tegmentum  of  the  crura  cerebri.  Posteriorly  from  the  nates 
two  bands  are  projected  by  which  the  corpora  quadrige- 
mina are  connected  with  the  cerebellum  behind  and  below; 
these  bands  are  known  as  the  iwocessus  ad  testes.  Above 
and  in  front  of  the  nates,  aiid  behind  the  posterior  commis- 
sure of  the  third  ventricle,  is  situated  a  small  oval  mass — 
the  pineal  gland. 

The  corpora  geniculata  are  the  two  rounded  masses  at 
the  outer  surface  of  the  posterior  end  of  the  optic  thalanii. 

The  General  Ventricular  Cavity  of  the  Cerebrum. 

This  cavity,  as  I  have  already  stated,  is  bounded  above  by 
the  under  surface  of  the  corpus  callosum;  laterally  by  the 
■cerebral  mass  in  its  upper  part  and  ]jy  the  optic  thalami  in 
the  lower  part;  beloiv  by  the  structures  contained  in  the 
interpeduncular  space.  This  cavity  is  divided  by  a  horizon- 
tal partition  into  an  upper  and  lower  part.  The  horizontal 
partition  is  formed  by  the  fornix  and  the  velum  interpositum. 

23 


354     LECTURES  ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  fornix  is  a  flat  lamella  of  white  matter  which  is 
projected  horizontally  into  the  general  ventricular  cavity 
a  little  beneath  the  under  surface  of  the  corpus  callosum. 
The  fornix  is  shaped  like  an  elongated  leaf.  Its  thin, 
tapering  portion  is  directed  backward  toward  the  posterior 
part  of  the  under  surface  of  the  corpus  callosum,  with 
which  it  is  connected.  The  broad  anterior  portion,  which 
is  termed  the  hody  of  the  fornix,  is  projected  horizontally 
forward  into  the  general  ventricular  cavity,  dividing  it  im- 
perfectly into  an  upper  and  lower  compartment.  From 
the  anterior  border  of  the  body  of  the  fornix  two  flat,  nar- 
row bands  are  projected  forward,  which  are  called  the 
anterior  crura  of  the  fornix.  These  pass  forward  and  arch 
downward  into  the  lower  part  of  the  general  ventricular 
cavity,  which  is  called  the  thh^d  ventricle.  They  pass  down 
through  the  space  between  the  genu  of  the  corpus  callosum 
in  front  and  the  anterior  extremity  of  the  optic  thalarai 
and  the  anterior  commissure  of  the  third  ventricle  behind. 
Descending  to  the  third  floor  of  the  ventricle,  they  sud- 
denly turn,  forming  the  two  rounded  masses,  called  the 
corpora  albicantia,  which  are  seen  at  the  base  of  the  brain 
in  the  interpeduncular  space.  From  these  the  fibres  of 
the  anterior  crura  ascend  and  enter  the  substance  of  the 
optic  thalami  at  the  inner  surface. 

Between  the  anterior  crura  of  the  fornix  and  the  ante- 
rior end  of  the  optic  thalamus  on  each  side  there  is  an  open- 
ing by  which  each  lateral  half  of  the  upper  portion  of  the 
general  ventricular  cavity  communicates  with  the  lower 
portion — viz.,  with  the  third  ventricle.  This  opening  on 
each  side  is  called  ih.e  foramen  of  Monro. 

The  posterior  tapering  end  of  the  fornix,  as  it  passes 
backward  toward  the  posterior  part  of  the  under  surface 
of  the  corpus  callosum,  also  divides  into  two  lateral  bands, 
which  are  called  the  x>osterior  piUai^s  of  the  crura  of  the 
fornix.  These  diverge  and  pass  backward  and  outward  ; 
their  posterior  end  then  descends  into  the  descending  horns 


THE   CEREBRUM.  355 

of  the  lateral  ventricles,  forming  part  of  their  floor.  The 
edges  of  the  posterior  crura  are  called  the  corjms  fimbria- 
tum.  The  triangular  space  between  the  diverging  poste- 
rior crura  behind  the  body  of  the  fornix  is  termed  the  lyra; 
it  is  filled  with  the  velum  interpositum. 

The  velum  interpositum  is  a  prolongation  of  the  pia 
mater.  It  enters  the  general  ventricular  cavity  through 
the  narrow  space  between  the  under  surface  of  the  poste- 
rior end  or  splenium  of  the  corpus  callosum  and  the  upper 
surface  of  the  corpora  quadrigemina  and  the  pineal  gland. 

In  the  general  ventricular  cavity  this  prolongation  of  the 
pia  mater  expands  horizontally  along  the  under  surface  of 
the  fornix.  The  edges  of  the  velum  interpositum  are  highly 
vascular  and  present  small  villous  projections  ;  this  is 
termed  the  choroid  plexus.  It  passes  forward  between  the 
edge  of  the  fornix  and  the  optic  thalamus,  forming  a  part 
of  the  floor  of  the  central  cavity  of  the  lateral  ventricle  on 
each  side.  Posteriorly  the  choroid  plexus  descends  into 
the  middle  horn  of  the  lateral  ventricle  on  each  side,  form- 
ing a  part  of  the  floor. 

The  general  ventricular  cavity  is  thus  completely  divided 
into  an  upper  and  lower  compartment  by  the  fornix  and 
the  velum  interpositum  just  described. 

The  upper  portion  of  the  general  ventricular  cavity  is 
again  divided  into  lateral  halves,  called  the  lateral  ven- 
tricles, by  a  vertical  septum  which  is  called  the  septum  luci- 
dum. 

The  septum  lucidum  is,  as  I  have  just  stated,  a  vertical 
septum  which  separates  the  two  lateral  ventricles  from 
each  other.  This  septum  consists  of  two  layers  of  a  thin 
membrane,  which  is  attached  below  to  the  upper  surface  of 
the  fornix,  in  front  to  the  reflected  portion  of  the  genu  of 
the  corpus  callosum,  above  to  the  under  surface  of  the  cor- 
pus callosum. 

The  Fifth  Ventricle. — The  interval  between  the  two 
layers  of  the  septum  lucidum  is  called  the  fifth  ventricle. 


356     LECTURES   ON   HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

This  cavity  is  not  lined  with  epithehum  and  does  not  com- 
municate with  the  other  parts  of  the  general  ventricular 
cavity. 

The  Lateral  Ventricles. — The  cavities  lateral  to  the  sep- 
tum lucidum,  and  above  the  fornix  and  the  velum  inter- 
positum,  are  called  the  lateral  ventricles.  They  are  serous 
•cavities,  lined  by  a  thin  membrane  covered  with  a  layer  of 
ciliated  epithelium;  this  membrane  is  called  the  ependyina. 
The  lateral  ventricles  contain  serous  fluid.  Each  lateral 
ventricle  consists  of  a  central  cavity  and  three  smaller 
■cavities  or  cornua,  which  are  called  the  anterior,  posterior, 
■and  middle  or  descending  cornu  or  horn. 

The  central  cavity  of  the  lateral  ventricle  is  triangular  in 
form;  its  roof  is  formed  by  the  under  surface  of  the  corpus 
callosum,  its  inner  wall  by  the  septum  lucidum,  its  floor 
by  various  structures  w^hich  pass  backward  and  may  be 
enumerated  as  follows:  the  upper  surface  of  the  nucleus 
caudatus  of  the  corpus  striatum;  the  taenia  semicircularis; 
the  upper  surface  of  the  optic  thalamus;  the  choroid  plexus 
of  the  velum  interpositum;  the  fornix,  and  a  part  of  the 
corpus  fimbriatum,  or  edge  of  the  posterior  cms  of  the  for- 
nix on  that  side. 

The  anterior  cornu  of  the  lateral  ventricle  is  triangular, 
and  passes  from  the  central  cavity  forward  and  outward 
into  the  substance  of  the  frontal  lobe.  It  is  bounded  above 
by  the  under  surface  of  the  corpus  callosum;  externally  by 
the  caudate  nucleus  of  the  corpus  striatum;  and  internally 
and  ui  front  by  the  reflected  portion  of  the  anterior  end  of 
the  corpus  callosum. 

The  posterior  cornu  of  the  lateral  ventricle  is  also  trian- 
gular and  pointed;  it  passes  backward  in  the  occipital  lobe; 
its  direction  is  backward,  outward,  and  then  inward. 

The  inner  wall  of  the  posterior  cornu  is  formed  by  a 
longitudinal  elevation  called  the  hii^pocanipus  major.  This 
elevation  is  formed  by  the  extension  of  the  calcarine  sulcus 
which  is  seen  on  the  lower  part  of  the  inner  surface  of  the 


THE   CEREBRUM.  357 

cerebral  hemisphere.  The  walls  of  this  cavity  are  formed 
by  the  substance  of  the  occipital  lobe  of  the  cerebral  hemi- 
sphere. 

The  descending  cornu  of  the  lateral  ventricle  passes  down- 
ward around  the  posterior  end  of  the  optic  thalamus  into 
the  substance  of  the  middle  lobe  of  the  cerebral  hemi- 
sphere. 

The  descending  horn  is  triangular  and  pointed;  it  ex- 
tends backward,  outward,  and  downward,  and  curves  for- 
ward and  inward,  its  point  terminating  close  to  the  fissure 
of  Sylvius.  Its  roof  is  formed  by  transverse  fibres  of  the 
corpus  callosum,  and  its  sides  by  the  mass  of  the  temporo- 
sphenoidal  lobe.  Its  floor  is  formed  by  the  following  struc- 
tures: the  hippocampus  major;  the  pes  hippocampi;  the 
eminentia  collateralis;  the  corpus  fimbriatum  of  the  pos- 
terior crus  of  the  fornix  ;  the  choroid  plexus  of  the  velum 
interpositum;  the  fascia  dentata,  and  the  transverse  fissure. 

The  hippocampus  major  is,  as  I  have  already  stated,  an 
elevation  produced  by  an  extension  of  the  calcarine  sulcus. 

The  pes  hippocampi  is  the  lower  end  of  this  elevation;  it 
presents  several  furrows,  so  that  it  resembles  an  animal's 
paw. 

The  eminentia  coUatercdis,  or  pes  accessorius,  is  an 
elevation  seen  at  the  junction  of  the  middle  and  the  pos- 
terior horn. 

The  fascia  dentata  is  a  serrated  band  of  gray  substance 
placed  between  the  choroid  plexus  and  the  corpus  fimbri- 
atum. 

The  transverse  fissure  is  horseshoe-shaped;  it  passes 
from  the  apex  of  the  descending  horn  of  the  lateral  ven- 
tricle on  one  side  to  that  on  the  other  side. 

This  fissure  passes  from  the  apex  of  the  middle  horn  up- 
ward and  backward,  and  then  horizontally  across  to  the 
other  side,  and  on  that  side  again  forward  and  downward 
to  the  apex  of  the  uiiddle  horn  of  the  other  side. 

The  portion  of  the  fissure  which  passes  from  the  apex  of 


358      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

the  horn  upward  and  backward  is  bounded  above  by  the 
optic  thalarai,  below  by  the  corpus  fi  nib  datum  of  the  pos- 
terior crus  of  the  fornix. 

The  horizontal  portion  of  the  fissure  is  bounded  above 
by  the  under  surface  of  the  posterior  end  of  the  corpus  cal- 
losuni,  and  below  by  the  posterior  surface  of  the  corpora 
quadrigemina.  Through  this  fissure  prolongations  of  the 
pia  mater  enter  the  general  ventricular  cavity. 

Tlte  Third  Ventricle. — The  narrow^,  oblong  space  be- 
neath the  fornix  and  between  the  inner  surfaces  of  the 
optic  thalami  is  called  the  third  ventricle.  The  roof  of 
this  cavity  is  formed  by  the  under  surface  of  the  velum 
interpositum  and  its  choroid  plexus  on  each  side;  its  lateral 
walls  by  the  inner  surfaces  of  the  optic  thalami;  its  floor 
by  the  parts  filling  the  interpeduncular  space.  In  front 
the  cavity  is  bounded  by  the  anterior  end  of  the  corpus 
callosum  and  by  the  anterior  commissure;  posteriorly  it 
is  bounded  by  the  posterior  commissure. 

The  cavity  of  the  third  ventricle  is  traversed  by  three 
commissures,  called  the  anterior,  middle,  and  posterior 
commissures. 

The  anterior  commissure  forms  the  anterior  boundary  of 
the  cavity;  it  is  a  transverse  band  of  white  fibres  and  con- 
nects the  corpora  striata. 

The  middle  commissure  is  a  transverse  band  of  gray 
matter  which  connects  the  optic  thalarai  in  the  middle, 

Hhe  posterior  commissure  forms  the  posterior  boundary 
of  the  cavity;  it  is  a  transverse  band  of  white  fibres  which 
connect  the  optic  thalami  behind.  The  third  ventricle  cora- 
municsiteshj  i\\Q  foramen  of  Monro  with  the  lateral  ven- 
tricles above;  behind  and  below  it  communicates  with  the 
fourth  ventricle  by  the  aqueduct  of  Sylvius,  which  is  also 
called  the  iter  a  tertio  ad  qnartum  ventricnhun.  In  the 
middle  of  its  floor  it  communicates  by  an  opening  with  the 
tubular  process  of  the  infundibulum,  and  through  this 
with  the  interior  of  the  pituitary  body. 


LECTUEE  XXXVIIL 

THE  STRUCTURE  OF  THE  CEREBRUM. 

The  cerebrum  is,  like  all  central  organs  of  the  nervous 
system,  composed  of  gray  and  of  white  nerve-substance. 
The  gray  substance  of  the  cerebrum  comprises: 

1.  That  of  the  cortex. 

2.  That  of  the  basal  ganglia. 

3  That  which  lines  various  portions  of  the  general  ven- 
tricular cavity. 

1.   The  Gray  Matter  of  the  Cortex. 

The  gray  matter  which  fomis  the  cortical  substance  of 
the  cerebrum,  covers  it  in  a  nearly  equal  thickness  ;  it  also 
covers  the  walls  of  the  sulci  and  fissures. 

This  gray  matter,  with  the  exception  of  that  in  certain 
regions  of  the  cerebral  hemispheres,  is  arranged  in  five 
distinct  layers. 

These  five  layers  are  arranged  as  follows:  The  first  or 
outer  layer  consists  of  a  stratum  of  neurogha  which  is 
permeated  by  a  delicate  fibrillar  network,  and  scattered 
between  this  are  small  ganglion  or  nerve  cells. 

The  second  layer  consists  of  numerous  small  pyramidal 
cells,  which  are  closely  packed  together  and  so  form  a 
dense  structure. 

The  third  layer  also  consists  of  numerous  pyramidal 
cells,  but  they  are  not  closely  packed  as  in  the  previous 
layer  ;  they'  increase  in  size  in  the  deeper  parts.  This 
layer  is  the  thickest  of  the  five. 

The /o?<rf72  layer  is  composed,  like  the  second,  of  small, 
densely  packed,  irregular  cells.     Owing  to  the  triangular  or 


360     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

irregular  form,  this  layer  appears  granular,  hence  the  name 
granular  formation.  The  fifth  layer  consists  of  large,  spin- 
dle-shaped, oblong  ganglion-cells. 

As  before  stated,  there  are  certain  locations  in  which 
the  cortical  substance  is  not  arranged  in  five  distinct  layers. 
The  exceptional  locations  are,  according  to  Meynert,  the 
following  : 

(rt)  Tlie  cortical  substance  of  the  posterior  part  of  the 
occipital  lobe.  This  consists  of  eight  layers;  the  additional 
three  layers  are  composed  of  strata  of  densely  packed  cells 
as  in  the  second  layer;  they  are  interposed  between  the 
other  five  layers. 

(6)  The  cortical  substance  of  the  hippocampus  major. 
This  consists  of  layers  of  cells  identical  in  form  and  arrange- 
ment with  those  of  the  third  layer.  The  fourth  and  fifth 
layers  are  absent  in  this  region. 

(c)  The  cortical  substance  of  the  walls  of  the  fissure  of 
Sylvius.  This  consists  of  pyramidal,  spindle-shaped,  and 
elongated  cells  similar  to  those  found  in  the  fifth  layer. 
The  ctaustrnni,  or  collection  of  gray  matter  at  the  bottom, 
of  the  fissure  of  Sylvius,  is  composed  of  such  cells.  The 
claustrum  is  located  externally  to  the  external  capsule,  be- 
tween this  and  the  white  matter  of  the  island  of  Eeil. 

(d)  The  gray  matter  of  the  olfactory  bulbs,  which  are 
situated  near  and  attached  to  the  inferior  surface  of  the 
anterior  lobes  on  each  side  along  the  longitudinal  fissure. 
This  consists  above  of  white  matter  and  below  of  gray, 
the  latter  formed  of  layers  of  cells  and  medullated  fibres 
intermingled  with  small  cells. 

The  ganglion  or  nerve  cells  of  the  cerebral  cortical  sub- 
stance differ  in  form,  size,  and  arrangement  in  the  various 
layers.  They  have  no  cell- wall,  and  one  or  more  nuclei; 
they  are  either  irregular,  pyramidal,  stellate,  or  spindle 
shape  in  form,  and  have  one  or  more  poles. 

The  pole  of  the  unipolar  nerve  or  ganglion  cells  is  gene- 
rally continuous   with  the  axis-cylinder  of  a  nerve-fibre 


THE   STRUCTURE    OF   THE   CEREBRUM.  361 

of  the  poles  of  the  multipolar  ganglion-cells.  One  ascends 
into  the  upper  layer  of  cells  and  communicates  with  the 
fibres  of  the  network  of  the  outer  layer;  this  is  termed 
the  process  of  the  aj^ex.  Another  pole,  termed  the  process 
of  the  centre  of  the  base,  is  directed  downward  toward  the 
white  substance  of  the  cerebrum  and  is  continuous  with 
the  axis-cylinder  of  a  nerve-fibre.  The  other  poles,  called 
the  lateral  processes,  form  the  delicate  fibrillar  network  of 
the  cortical  gray  substance. 

2.   TJie  Gray  Matter  of  the  Basal  Ganglia. 

{a)  The  gray  matter  of  the  corpus  striatum — viz.,  that 
of  the  nucleus  caudatus  and  the  nucleus  lenticularis— con- 
sists of  multipolar  nerve- cells  of  different  sizes;  generally 
those  of  the  nucleus  lenticularis  are  larger. 

The  two  masses  of  the  corpus  striatum  are  traversed  by 
medullated  nerve-fibres.  Other  fibres  arise  from  the  cells 
of  the  masses,  and,  passing  out  of  them,  pass  toward  the 
periphery  of  the  hemispheres. 

ih)  The  gray  matter  of  the  optic  thalamus  is  composed 
of  large,  elongated,  multipolar  cells.  It  is  arranged  in  two 
masses— viz.,  the  internal  and  the  external  nucleus.  The 
two  are  separated  by  a  central  septum  of  white  nerve-sub- 
stance; a  thin  layer  of  this  also  covers  the  exterior  of  the 
optic  thalamus. 

(c)  The  gray  matter  of  the  corpora  quadrigemina  consists 
of  a  peripheral  layer  and  of  a  central  mass;  the  latter  con- 
stitutes part  of  the  gray  matter  of  the  general  ventricular 
cavity.  The  peripheral  layer  constitutes  a  part  of  the 
basal  gray  matter;  it  consists  of  small  multipolar  cells  of 
a  delicate  fibrillar  network;  the  outer  surface  is  covered  by 
a  thin  layer  of  white  substance.  The  gray  matter  of  the 
nates,  or  anterior  lobes  of  the  corpora  quadrigemina,  con- 
sists of  two  layers — the  outer,  or  stratum  cinereum,  and  the 
deeper,  or  stratum  opticum ;  the  latter  consists  of  fine, 
longitudinal  fibres  and  small  multipolar  cells  embedded  in 


362     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

these.     This  stratum  is  separated  from  the  central  gray 
mass  by  a  thin  layer  of  white  substance. 

The  peripheral  gray  matter  of  the  testes,  or  posterior 
lobes  of  the  corpora  quadrigemina,  is  separated  from  the 
central  gray  mass  by  a  transverse  layer  of  white  fibres. 

(d)  The  gray  matter  of  the  corpora  geniculata  is  continu- 
ous with  that  of  the  optic  thalamus.  It  consists  of  multi- 
polar nerve-cells,  those  of  the  external  geniculate  bodies, 
containing  pigment  granules  which  give  them  a  dark 
color. 

(e)  The  gray  substance  of  the  locus  niger  consists  of 
small  multipolar  cells,  which,  owing  to  the  presence  of 
many  pigment-granules,  have  a  very  dark  color,  hence  the 
name. 

3.   The   Gray  Matter  Lining  Parts  of  the  General 
Ventricular  Cavity  of  the  Cerebrum. 

The  gray  substance  of  this  group  includes  the  following: 

{a)  The  gray  matter  which  covers  the  internal  surface  of 
the  optic  thalami  and  lines  the  lateral  walls  and  floors  of 
the  third  ventricle. 

(6)  That  which  forms  the  gray  or  middle  commissure  of 
the  third  ventricle. 

(c)  That  which  forms  the  gray  structures  enclosed  in  the 
interpeduncular  space — viz.,  the  tuber  cinereum,  the  infun- 
dibulum,  and  the  posterior  perforated  space. 

{d)  That  which  covers  the  superior  surface  of  the  teg- 
mentum of  the  crura  cerebri. 

{e)  The  central  gray  mass  of  the  corpora  quadrigemina. 
This  forms  the  upper  and  posterior  wall  of  the  aqueduct  of 
Sylvius;  it  is  composed  of  large  multipolar  cells  which  are 
the  origin  of  the  third  and  fourth  pairs  of  cranial  nerves. 

The  gray  matter  distributed  to  these  various  parts  of  the 
general  ventricular  cavity  of  the  cerebrum  is  continuous 
with  that  lining  the  aqueduct  of  Sylvius;  this  is  again  con- 
tinuous with  that  covering  the  floor  of  the  fourth  ventricle, 


THE   STRUCTURE    OF   THE   CEREBRUM.  363 

and  this  with  the  gray  matter  of  the  spinal  cord.  The  gray 
matter  in  the  various  parts  of  the  general  yentricular  cavity 
is  composed  of  nerve-cells  and  dehcate  fibrillae. 

Tlie  White  Nerve- Substcmce  of  the  Cerebrum. 

This   structure   consists  of  medullated  nerve-fibres,  and 
composes  the  main  portion  of  the  interior  of  the  cerebrum. 
The  nerve-fibres  are  arranged  in  three  groups — viz.: 

1.  The  corona  radiata. 

2.  The  commissural  fibres  which  pass  transversely  be- 
tween the  two  hemispheres. 

3.  The  commissural  fibres  which  connect  various  parts  in 
one  hemisphere, 

1.  The  Corona  Radiata. — The  corona  radiata  is  a  system 
of  medullated  nerve-fibres  which,  in  the  cerebral  hemi- 
•spheres,  radiate  toward  their  periphery,  where  they  con- 
nect with  the  ganglia  of  the  cortical  substance. 

The  fibres  of  the  corona  radiata  may  be  divided  into  (a) 
Xiortico-xjetal  fibres,  viz.,  those  which  pass  to  the  ganglia 
in  the  cortical  substance;  and  (6)  cortico-fugal  fibres,  viz., 
those  which  arise  from  the  cortical  ganglia. 

These  fibres  which  radiate  in  the  cerebral  hemispheres 
enter  and  leave  the  cerebrum  at  its  base,  and,  according  to 
their  derivation,  they  may  be  classified  into : 

(a)  Those  from  the  crusta,  or  inferior  stratum  of  the  crura 
cerebri. 

(Jb)  Those  from  the  tegmentum,  or  superior  stratum  of 
the  crura  cerebri. 

(c)  Those  arising  from  the  ganglia  of  the  locus  niger, 
the  middle  layer  of  the  crura  cerebri. 

{d)  Those  arising  from  the  gangha  of  the  gray  matter 
which  forms  the  posterior  part  of  the  aqueduct  of  Sylvius. 

The  fibres  from  these  various  sources  enter  the  hemi- 
spheres and  pass  upward.  Some  of  them  radiate  directly 
to  the  cortical  substance,  ascending  through  the  external 
and  internal    capsule    between  the  large    basal   ganglia. 


364     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

Others,  again,  enter  and  penetrate  these  gangha — viz.,  the 
corpus  striatum  and  optic  thalamus.  Tlie  fibres  radiating 
toward  the  cortex  above  these  gangha  are  joined  by  many 
fibres  which  arise  from  the  cells  in  the  ganglia. 

The  fibres  of  the  crusta  and  of  the  tegaientum  are  con- 
tinuous with  fibres  of  the  pons  Varolii,  and  these  again  are 
continuous  with  fibres  of  the  various  parts  of  the  medulla 
oblongata,  as  follows: 

Those  longitudinal  fibres  of  the  pons  which  are  continued 
upward,  as  the  fibres  of  the  crusta,  or  inferior  stratum  of 
the  crura  cerebri,  are  derived  from  the  pyramids  of  the 
medulla  oblongata. 

The  fibres  of  each  pyramid  of  the  medulla  are  continuous 
with  (a)  those  of  the  direct  pyramidal  tract  of  the  anterior 
column  of  the  spinal  cord  on  the  same  side,  and  {b)  those 
of  the  crossed  pyramidal  tract  of  the  lateral  column  of  the 
cord  from  the  opposite  side. 

The  fibres  of  the  various  portions  and  fasciculi  of  the 
spinal  cord  ascend,  forming  the  pyramids  of  the  medulla; 
the  fibres  of  the  pyramids  are  continued  upward  to  form 
the  fibres  of  the  crusta  of  the  crura  cerebri. 

Those  longitudinal  fibres  of  the  pons  which  are  contin- 
ued upward,  as  the  fibres  of  the  tegmentum  of  the  crura 
cerebri,  are  derived  from  the  format  io  reticular  is  of  the 
medulla.  This  is  a  network  of  longitudinal  and  transverse 
fibres  contained  in  the  substance  of  the  medulla;  they  are 
derived  from  the  funiculus  cuneatus  and  the  funiculus 
gracilis  of  the  medulla,  from  the  olivary  body  of  the  me- 
dulla, and  from  the  anterior  column  of  the  spinal  cord. 

The  fibres  of  the  tegmentum  enter  and  penetrate  the 
optic  thalami,  and  radiate,  together  with  fibres  arising  from 
the  cells  of  the  optic  thalami,  toward  the  cortical  substance 
of  the  temporosphenoidal  and  occipital  lobes. 

2.  The  Commissural  Fibres  which  pass  transversely  be- 
tiveen  the  two  Hemispheres. — The  fibres  of  this  group 
include  : 


THE    STRUCTURE   OP   THE   CEREBRUM.  365 

(a)  The  fibres  of  the  corpus  callosum. 

(6)  The  fibres  of  the  anterior  commissure  of  the  third 
ventricle. 

(c)  The  fibres  of  the  posterior  commissure  of  the  third 
T'entricle. 

(a)  The  fibres  of  the  corpus  callosum  pass  transversely 
across  from  one  cerebral  hemisphere  to  the  other;  in  the 
hemispheres  they  radiate  toward  the  cortical  substance. 

(b)  The  fibres  of  the  anterior  commissure  pass  trans- 
versely through  the  third  ventricle  in  front  of  the  anterior 
■crura  of  the  fornix.  These  fibres  pass  through  the  corpus 
striatum  in  each  hemisphere,  and  then  pass  backward  into 
the  temporo-sphenoidal  lobe. 

(c)  The  fibres  of  the  posterior  commissure  pass  trans- 
versely across  the  posterior  part  of  the  third  ventricle; 
some  of  them  are  derived  from  the  tegmentum  on  one 
side.  They  then  pass  across  the  third  ventricle,  and  then 
into  the  temporo-sphenoidal  lobe.  Others  pass  across  the 
third  ventricle,  connecting  the  optic  thalami  on  both  sides. 

3.  The  Commissural  Fibres  ivliich  connect  various  Parts 
in  one  Hemisphere  of  the  Cerebrum. — The  fibres  of  this 
group  are: 

{a)  The  fibres  of  the  fornix,  which  connect  the  optic 
thalami  with  the  hippocampus  major. 

(5)  The  tcenia  semicircular  is,  which  separate  the  optic 
thalamus  from  the  nucleus  caudatus.  These  fibres  pass 
from  the  anterior  crura  of  the  fornix  upward  toward  the 
roof  of  the  middle  horn  of  the  lateral  ventricle. 

(c)  The  longitudinal  fibres  of  the  corpus  callosum. 

{d)  The  unciiiate  fascicidus  are  bundles  of  fibres  which 
connect  the  convolutions  of  the  frontal  with  those  of  the 
temporo-sphenoidal  lobes. 

(e)  The  inferior  longitudinal  fasciculus — a  bundle  of 
fibres  which  connect  the  temporo-sphenoidal  with  the 
occipital  lobe. 

(/)  The  fillet  of  the  gyrus  fornicatus — a  band  of  fibres 


366     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

which  begin  in  front  in  the  anterior  perforated  space,  then 
pass  upward,  winding  over  the  anterior  extremity  of  the 
corpus  callosum,  and  then  arching  backward  parallel  with 
the  rostrum  of  the  corpus  callosum,  and  continue  in  its 
convolutions  ;  the  fibres  then  curve  downw^ard  over  the 
posterior  extremity  of  the  corpus  callosum,  and  pass  for- 
ward in  the  substance  of  the  temporo-sphenoidal  lobe 
again  to  the  anterior  perforated  space. 

(g)  The  arcuate  or  association  fibres  are  arching  fibres 
which  connect  the  central  substance  of  the  hemispheres 
beneath  their  convolutions. 


LEOTUEE  XXXIX. 

THE  FUNCTIONS  OF  THE  CEREBRUM. 

The  cerebrum  is  the  seat  of  intelligence.  All  psycho- 
logical processes,  such  as  thinking,  feeling,  remember- 
ing, judging,  the  perception  and  retention  of  all  sensorial 
impressions,  and  all  actions  and  functions  which  i-equire 
thought,  decision,  or  psychical  effort,  are  dependent  upon 
the  normal,  harmonious  activity  and  healthy  condition  of 
the  cerebrum. 

The  functions  of  the  cerebrum  have  been  studied  by  ob- 
servation of  the  effects  produced  by  irregularities  and  by 
pathological  lesions  of  the  cerebrum  or  of  parts  of  it,  and 
more  definite  studies  have  been  made  by  experiments 
made  on  animals. 

It  is  well  known  that  individuals  having  a  microce- 
phalon — a  condition  characterized  by  a  small  development 
of  the  brain,  and  principally  of  the  cerebrum— possess  a 
very  low  degree  of  intelligence  and  are  generally  idiots 
and  cretins.  The  same  is  often  observed  in  individuals 
suffering  from  hydrocephalus.  The  psychical  activities 
are  more  or  less  impaired  or  totally  absent  in  individuals 
with  injuries  and  pathological  lesions  of  the  cerebrum — as, 
for  instance,  degenerations,  new  growths,  inflammations, 
pressure,  or  interference  with  the  blood-supply.  Drugs 
known  as  narcotics  also  suppress  the  psychical  functions 
and  processes. 

Removal  of  the  cerebrum  of  animals  is  followed  by  a 
total  loss  of  all  intelligence.  The  animal  loses  the  power 
of  voluntary  motility;  it  loses  the  power  to  perceive  and 
retain  sensory  impressions,  and  it  also  loses  the  sense  of 


368     LECTUKES   ON   HUMAN    PHYSIOLOGY   AND   HISTOLOGY. 

sight,  smell,  hea.ring,  touch,  and  of  common  sensation. 
The  animal  becomes  a  mere  machine;  it  is  incapable  of 
retaining  its  equilibrium;  it  makes  a  few  walking  motions 
when  pushed;  it  swallows  when  food  is  forced  into  its 
pharynx,  and  it  performs  all  such  functions  and  actions 
that  are  ordinarily  reflex. 

The  many  observations  and  experiments  which  have 
been  made  to  determine  the  functions  of  the  cerebrum 
have  shown  the  following: 

1.  That  the  degree  of  intelligence  of  the  individual  de- 
pends upon  the  degree  of  the  development  of  the  cerebral 
hemispheres  as  compared  with  the  other  parts  of  the 
brain. 

2.  That  the  degree  of  intelligence  depends  upon  the  corti- 
cal gray  substance  of  the  cerebral  hemispheres  and  upon 
its  extent  and  development. 

The  Functions  of  the  Various  Parts  of  the  Cerebrum. 

A.  The  Functions  of  the  Gray  Cortical  Substance. — The 
general  function  of  the  gray  cortical  substance  of  the 
cerebral  hemispheres  is  to  control  all  psychical  processes, 
such  as  the  production  of  the  co-ordinated  complex  motions 
which  are  brought  about  by  an  effort  of  the  will  and  with 
a  certain  purpose — as,  for  instance,  the  motions  concerned 
in  the  act  of  speaking,  by  which  ideas  are  expressed  in 
words  ;  again,  processes  such  as  the  understanding  of 
sounds  and  language,  the  recognition  of  sights,  etc. 

It  was  formerly  believed  that  these  functions  were 
equally  possessed  by  all  parts  of  the  cortical  gray  substance 
of  the  cerebral  hemispheres,  and  that  if  any  part  was  de- 
stroyed the  remaining  parts  would  take  up  its  function,  so 
that  no  disturbance  of  any  of  the  functions  was  produced. 
Later  experiments  have  shown,  however,  that  this  theory 
is  erroneous,  and  that  the  seats  for  the  various  functions 
are  localized  in  various  parts  of  the  cortical  gray  substance. 

Many  experiments  and  observations  have  been  made  to 


THE   FUNCTIONS   OF   THE   CEREBRUM.  369 

localize  the  vaiious  functions  and  to  map  out  the  areas  on 
the  exterior  of  the  cerebral  hemispheres.  In  animals  this 
was  done  by  the  gradual  and  methodical  removal  of  parts 
of  the  cortical  gray  substance  and  observing  the  effects 
resulting  from  this.  In  man,  observation  of  the  effects 
produced  by  lesions  in  parts  of  the  cerebral  cortical  gray 
substance  aided  in  localizing  the  exact  seat  of  many  func- 
tions. The  method  most  employed  is  the  stimulation  of 
the  various  regions  of  the  cortical  gray  substance  by  the 
application  of  weak  electric  currents  and  observing  the 
effects  so  produced. 

Scientists  who  made  this  a  special  subject  for  their 
studies  and  experiments  have  thus  succeeded  in  localizing 
many  of  the  functions — a  fact  which  is  most  valuable  for 
the  localization  of  injuries  and  pathological  lesions  of  the 
cerebral  hemispheres. 

The  areas  which  are  the  seat  of  the  various  functions  of 
the  cortical  gray  substance  have  thus  been  located  and 
mapped  out  on  the  surface  of  the  cerebral  hemispheres  as 
follows: 

I.  The  cortical  or  psycho -motorial  centres  are  located  in 
an  area  which  includes  the  posterior  part  of  the  frontal 
lobes  and  the  middle  and  superior  regions  of  the  parietal 
lobes.  The  psycho-motorial  centres  are  those  which  govern 
the  co-ordinated  contractions  of  the  muscles  employed  in 
the  production  of  voluntary  motion, 

'  These  cortical  motor  centres  for  the  various  groups  of 
muscles  are  located  in  the  following  circumscribed  regions 
of  this  area: 

1.  The  centre  for  the  extensors  of  the  arms  and  hands 
is  located  in  the  posterior  part  of  the  superior  and  middle 
frontal  convolutions,  near  the  margin  of  the  pre-central 
sulcus. 

2.  The  centres  for  the  rotation  of  the  hands  and  for  the 
flexion  of  the  forearm  are  located  just  above  the  centres 
for  the  elevation  and  depression  of  the  angles  of  the  mouth, 

24 


370     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

viz.,   in  the  mid-portion  of  the   ascending  frontal  convo- 
lutions. 

3.  The  centres  for  the  movements  of  the  ivrists  and 
fingers  are  located  in  the  ascending  parietal  convolutions. 

4.  The  centres  for  the  movements  of  the  hands  and  feet 
are  located  in  the  superior  parietal  convolutions,  near  the 
posterior  central  sulcus. 

5.  The  centres  for  the  complex  movements  of  the  arms 
and  legs — as,  for  instance,  the  motions  by  which  swimming 
is  effected — are  located  in  the  upper  portion  of  the  ascend- 
ing frontal  convolutions,  near  the  longitudinal  fissure. 

6.  The  centres  for  the  movements  of  the  eyes  are  located 
in  the  middle  frontal  convolutions,  near  the  margin  of  the 
pre-central  sulcus. 

7.  The  centres  for  the  elevation  and  depression  of  the 
angles  of  the  month  are  located  in  the  middle  portion  of 
the  ascending  frontal  lobes. 

8.  The  centres  for  the  retraction  of  the  angles  of  the 
mouth  are  located  in  the  lower  portion  of  the  ascending 
frontal  lobes  or  convolutions,  just  above  the  ascending  limb 
of  the  fissure  of  Sylvius. 

9.  The  centres  for  the  movements  of  the  lips  and  tongue 
are  located  in  the  inferior  frontal  and  in  the  lower  part  of 
the  ascending  frontal  convolutions,  near  the  margin  of  the 
pre-central  sulcus. 

10.  The  centre  for  the  motions  of  speech  is  located  in  the  . 
lower  part  of  the  ascending  frontal   convolution   and  in 
the  island  of   Reil,  around  the  fissure  of  Sylvius  and  the 
pre-central  sulcus. 

It  has  been  observed  that  a  condition  known  as  aphasia, 
which  is  characterized  by  the  inability  te  express  ideas  in 
language,  is  produced  by  disease  or  lesions  of  this  region 
on  the  left  cerebral  hemisphere,  and  it  is  therefore  believed 
that  the  speech  centre  is  located  in  this  region  only.  The 
iesion  which  i^roduces  aphasia  does  not  produce  paralysis 
of  the  muscles  of  speech,  but  it  produces  a  disturbance  of 


THE   FUNCTIONS   OF   THE   CEREBRUM.  371 

the  co-ordiDated  harmonious  motions  of  these  muscles  that 
are  essential  for  articulate  speech. 

Irritation  of  the  various  motor  regions  of  the  cortical 
substance  of  one  cerebral  hemisphere  jDroduces  contractions 
of  the  described  muscle  groups  on  the  opposite  side  of  the 
body.  This  shows  that  the  cortical  substance  of  these 
various  regions  contains  motor  centres  for  these  respec- 
tive muscle  groups.  In  the  cortical  substance  of  these 
regions  are  large  pyramidal  ganglion  cells,  the  descending 
poles  of  v^hich  are  continuous  with  the  axis- cylinder  of 
the  motor  nerve-fibres  of  the  corona  radiata.  That  these 
ganglia  are  the  centres  for  these  nerve-fibres  is  shown  by 
the  fact  that  these  fibres  degenerate  and  lose  their  irrita- 
bility when  the  centres  are  destroyed  or  removed.  Irrita- 
tion of  the  fibres  of  the  corona  radiata  beneath  the  cortical 
motor  regions  produces  the  same  motions  as  direct  irrita- 
tion of  the  cortical  substance  of  these  regions. 

Strong  irritation  of  the  cortical  substance  of  the  motor 
region  produces  convulsive  muscular  contractions  ;  this 
is  often  observed  in  pathological  lesions  of  the  cortical 
motor  areas  which  cause  irritation  ;  the  convulsive  mus- 
cular contractions  so  produced  are  known  as  cortical  or 
Jacksonian  epilepsy. 

Irritation  of  the  cortical  motor  regions  by  the  applica- 
tion of  certain  chemicals,  such  as  the  ingredients  of  urine 
— viz.  J  keratin,  kreatinin,  urea,  etc. — also  produces  repeated 
clonic  and  tonic  convulsive  muscular  contractions  followed 
by  coma  or  total  loss  of  the  irritability  of  these  regions. 

It  is  believed  that  eclampsia  and  coma  of  uraemia  are  so 
produced  by  the  retention  of  such  urinary  ingredients  in 
the  system. 

Irritability  of  the  cortical  motor  regions  is  totally  sup- 
pressed in  the  condition  of  deep  narcosis  produced  by  the 
administration  of  alcohol,  ether,  chloroform,  morphine, 
etc.  These  drugs,  when  taken  in  small  doses,  at  first  in- 
crease the  irritabihty  of  the  motorial  regions.     In  the  con- 


372     LECTURES   ON    HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

dition  known  as  apnoea  and  asphijxia  the  irritability  of  the 
cortical  motorial  regions  is  also  suppressed. 

Slight  inflammatory  conditions,  slight  hyperaemia,  and 
a  small  loss  of  blood  increase,  while  a  large  loss  of  blood 
and  the  application  of  cold  decrease,  the  irritability  of  the 
cortical  motor  regions. 

Extirpation  or  destruction  of  the  cortical  motor  centres 
produces  peculiar  motorial  disturbances  of  the  respective 
muscle  groups,  in  that  the  motions  are  powerless  and  not 
co-ordinated  and  regular.  The  more  complicated  motions 
which  require  a  certain  psychical  effort  can  no  longer  be 
performed. 

The  motor  fibres  arising  from  the  cortical  motor  centres 
pass  downward  in  the  corona  radiata  through  the  internal 
capsule  ;  they  then  pass  to  the  crura  cerebri,  and  are  con- 
tained in  the  inferior  stratum  or  crusta  of  the  latter. 

Extirpation  of  the  cortical  centres  from  which  these 
nerv^e-fibres  arise  is  soon  followed  by  their  degeneration. 

II.  Psycho-sensorial  cortical  centres  are  located  in  an 
area  which  includes  (a)  the  area  of  the  cortical  psycho- 
motorial  centres,  and  (6)  the  superior  tempore  sphenoidal 
convolution,  the  lower  posterior  part  of  the  ascending 
parietal  convolution,  the  supramarginal  and  angular  por- 
tion of  the  inferior  parietal  convolution,  and  the  middle 
occipital  convolution. 

The  psycho-sensorial  centres  are  those  by  which  we  per- 
ceive the  impressions  of  sensible  things,  and  by  which  we 
recognize  the  character  of  such  impressions — as,  for  in- 
stance, the  impression  produced  by  the  firing  of  cannon, 
the  form  and  nature  of  the  things  we  touch,  the  nature  of 
odors,  sights,  and  sounds. 

The  centres  by  which  we  perceive  the  various  impres- 
sions of  sensible  things  are  located  in  certain  distinct, 
circumscribed  regions  of  the  above-described  area  of  the 
psycho-sensorial  centres.  Tlie  location  of  these  various 
regions  has  been  mapped  out  as  follows  : 


THE   FUNCTIONS   OF   THE   CEREBRUM.  373 

1.  The  cortical  or  psycho-sensorial  centres  for  the  seiise 
of  touch  and  common  sensations  of  the  various  parts  of  the 
body,  are  located  in  the  regions  of  the  cortical  substance 
which  are  the  seat  of  the  psycho  motorial  centres  for  the 
muscles  of  those  respective  parts  of  the  body. 

It  has  been  observed  that  the  motorial  disturbances  of  a 
certain  muscle-group,  produced  by  the  removal  of  the 
respective  psycho  motorial  centres,  is  accompanied  by  dis- 
turbances of  the  sense  of  touch  and  of  common  sensation 
in  the  region  of  that  muscle  group.  It  is  therefore  believed 
that  the  psycho  motorial  regions  for  certain  parts  of  the 
body  are  also  the  seat  of  the  centres  for  the  sense  of  toudi 
and  common  sensation  of  the  same  part  of  the  body. 

2.  The  cortical  or  psycho-sensorial  centre  for  the  sense  of 
sight  is  located  principally  in  the  middle  occipital  convolu- 
tion, but  the  visual  sphere  also  extends  upward  along  the 
cortex  of  the  angular  portion  and  along  that  of  the  supra- 
marginal  portion  of  the  inferior  parietal  convolution. 

Total  destruction  of  these  visual  spheres  produces  total 
blindness  ;  destruction  on  one  cerebral  hemisphere  pro- 
duces blindness  on  the  opposite  side.  The  visual  power 
does  not  return  when  the  visual  sphere  in  one  or  both 
hemispheres  is  totally  destroyed. 

Destruction  of  certain  parts  of  the  visual  sphere  causes 
a  decrease  of  the  visual  power  and  a  loss  of  the  power  to 
recognize  the  various  visual  impressions.  If,  in  a  dog,  a 
certain  portion  of  the  visual  sphere  is  destroyed,  the  ani- 
mal becomes  blind,  but  gradually  regains  a  certain  degree 
of  visual  power,  but  is  unable  to  recognize  the  objects 
which  are  brought  before  it.  It  has  been  observed  that 
this  condition,  when  it  is  produced  in  an  animal  by  experi- 
mental excision  of  certain  parts  of  the  visual  sphere,  grad- 
ually improves,  so  that  the  animal  again  learns  to  see  and 
recognize  various  objects.  This  is  believed  to  be  due  to 
the  fact  that  the  other  portions  of  the  visual  sphere  grad- 
ually assume  the  functions  of  the  removed  portion. 


374     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

3.  The  cortico-  or  psycho-sensorial  centre  for  the  sense 
of  hearing  is  located  in  the  superior  temporo-sphenoidal 
convolution,  near  the  margin  of  the  horizontal  limb  of  the 
fissure  of  Sylvius.  Destruction  of  the  cortical  substance 
in  this  region  produces  deafness  on  the  opposite  side.  De- 
struction of  certain  regions  of  this  sphere  causes  a  tem- 
porary loss  of  the  power  to  recognize  the  various  acoustic 
impressions. 

4.  The  cortical  or  psycho-sensorial  centres  for  smell  and 
taste  are,  according  to  Miink,  located  in  the  gyrus  hippo- 
campi. Destruction  of  the  cortical  substance  of  this  re- 
gion on  both  cerebral  hemispheres  causes  a  loss  of  smell 
and  taste.  The  exact  circumscribed  area  of  these  centres 
is  not  determined  as  yet. 

5.  The  presence  of  certain  cortical  thermal  centres  has 
been  detected  by  Eulenbery  and  Laudois.  They  have 
been  located  in  certain  psycho-motorial  regions  of  the 
frontal  and  parietal  lobes.  Experiments  and  observations 
show  that  in  these  regions  are  located  centres  which 
influence  the  temperature  of  certain  regions. 

The  sensory  nerves  which  communicate  and  are  con- 
nected with  these  various  cortical  or  psycho-sensorial 
centres  radiate  in  the  corona  radiata  and  pass  along  the 
internal  capsule.  Many  of  them  are  continuous  with 
those  of  the  tegmentum  ov  upper  stratum  of  the  crura 
cerebri. 

III.  The  cortical  centres  which  preside  over  the  higher 
psychical  functions  and  processes — such  as  thinking,  judg- 
ing, remembering,  deciding,  etc. — have  their  seat  in  the 
antero-lateral  regions  of  the  frontal  lobes  and  in  the  lower 
part  of  the  temporo-occipital  regions  of  the  cerebral  hemi- 
spheres. Numerous  clinical  observations  tend  to  show 
that  these  regions  are  the  seat  of  such  higher  psychical 
functions.  It  has  been  observed  that  in  weak-minded 
elderly  people,  or  in  those  of  a  low  grade  of  intelligence, 
these  regions  are  atrophied.     Weakness  of  mind,  loss  of 


THE   FUNCTIONS   OF   THE   CEREBEUM.  375 

intelligence,  and  even  idiocy,  are  often  caused  by  lesions  of 
the  frontal  lobes. 

B.  The  Functions  of  the  Basal  Ganglia  and  of  other  Parts 
of  tlie  Cerebrum. — 1.  The  function  of  the  corpus  striatum 
is  believed  to  be  that  of  a  motor  ganglion  which  is  inter- 
posed in  the  course  of  the  fibres  arising  from  the  cortical 
psycho-motorial  fibres.  This  theory  is  based  upon  clinical 
observations  and  on  physiological  experiments.  It  has 
been  observed  that  removal  or  pathological  lesions  of  the 
corpus  striatum  cause  hemiplegia — viz.,  the  inabihty  to 
perform  voluntary  muscular  contraction  on  the  opposite 
side  of  the  body. 

The  decussation  of  the  fibres  arising  from  the  psycho- 
motorial  or  cortical  centres  takes  place  beneath  the  corpus 
striatum. 

2.  The  function  of  the  ox^tic  thalamus  is  believed  to  be 
that  of  a  sensory  centre  interposed  in  the  course  of  the 
fibres  connected  with  the  cortical  psycho-sensorial  centres. 
This  is  only  a  theory  based  upon  clinical  observations  and 
the  results  obtained  by  physiological  experiments. 

Removal  and  certain  pathological  lesions  of  one  cerebral 
hemisphere  are  followed  by  loss  of  sensation  on  the  opposite 
side  of  the  body.  The  sensorial  fibres  passing  through  the 
optic  thalami  also  decussate  beneath  these. 

3.  The  functions  of  the  corpora  quaclrigemina  are  best 
explained  by  the  description  of  the  effects  produced  by 
their  removal  or  by  certain  pathological  lesions.  Removal 
of  the  corpora  quadrigemina  produces  total  blindness  of 
both  eyes.  Removal  of  one  produces  bhndness  of  the  eye 
on  the  opposite  side.  Removal  of  the  corpora  quadrige- 
mina produces  a  dilatation  of  the  iris  and  destroys  the  co- 
ordination of  the  movements  of  the  eyes. 

From  this  description  the  functions  of  the  corpora  quadri- 
gemina may  be  summed  up  as  follows: 

(a)  They  are  subcortical  centres  for  the  sense  of  sight. 


376     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

(6)  They  contain  centres  which  govern  the  movements 
of  the  iris. 

(c)  They  govern  the  co-ordinated  motions  of  the  eyes. 

4.  The  functions  of  the  corpora  geniculata  are  not  exactly 
knovs^n.  Their  removal  is  followed  by  disturbances  similar 
to  those  caused  by  the  removal  of  the  corpora  quadri- 
gemina. 

5.  The  functions  of  the  crura  cerebri  are  largely  those  of 
conducting  organs  :  the  fibres  of  the  crusta  conduct  motor 
impulses;  those  of  the  tegmentum,  sensory  impulses. 

The  middle  gray  substance  of  the  crura,  called  the  locus 
niger,  is  the  subcortical  centre  for  certain  complex  move- 
ments of  the  eyes.  From  these  centres  arise  the  third  cra- 
nial nerves,  through  w^hich  the  motorial  impressions  from 
these  centres  are  conducted  to  muscles  of  the  eyes. 

6.  The  functions  of  the  pituitary  body  and  the  pineal 
gland  are  unknown;  no  apparent  effect  is  produced  by 
their  removal. 

7.  The  functions  of  the  corpus  ccdtosuni,  and  of  the  com- 
missures in  the  third  ventricle,  are  to  connect  the  various 
parts  of  the  cerebral  hemisphere. 

8.  The  function  of  the  medullary  substance  of  the  cere- 
bral hemisphere  is  to  conduct  the  various  impressions  to, 
or  from,  or  between  the  various  structures  of  the  cerebral 
hemisphere. 

9.  The  function  of  the  fornix  is  probably  that  of  a  con- 
ducting organ. 

10.  The  functions  of  the  gray  nerve-structures  which  fill 
the  interpjeduacidar  space,  the  anterior  23erforcded  spaces, 
and  which  line  the  various  parts  of  the  ventricnlar  cavity 
of  the  cerebrum,  cannot  be  separately  described,  but  they 
are  probably  connected  with  the  functions  of  those  struc- 
tures of  gray  nerve- substance  with  which  they  are  in  con- 
tact. 

From  this  description  of  the  functions  of  the  various 
parts  of  the  cerebrum,  it  will  be  seen  that  it  is  a  complex 


THE   FUNCTIONS   OF   THE   CEREBRUM.  377 

structure  of  many  organs,  each  possessed  of  distinct  func- 
tions. Destruction  of  certain  parts  of  the  cerebrum  is  fol- 
lowed by  certain  characteristic  mental  or  physical  disturb- 
ances. 


LECTURE    XL. 

THE   CEREBELLUM. 

1.  Anatomy  and  Structure. 

The  cerebellum  is  that  portion  of  the  brain  which  oc- 
cupies the  posterior  fossae  of  the  cranium.  It  is  oval  in 
form  and  measures  about  3^  to  4  inches  in  its  lateral  and 
2i  inches  in  its  antero-posterior  diameter;  it  is  about  2 
inches  thick  in  the  centre,  and  gradually  becomes  thinner 
toward  its  periphery  or  margin.  The  weight  of  the  cere- 
bellum of  man  is  about  5^  ounces;  the  proportion  of  the 
cerebellum  and  the  cerebrum  is  about  1  to  8f . 

The  cerebellum  is  divided  into  an  upper  and  a  lower  part 
by  a  fissure  which  passes  around  the  margin  of  the  cerebel- 
lum; this  is  called  the  great  horizontal  fissure.  From  this 
several  fissures  or  sulci  pass  in  a  transverse  direction  over 
the  upper  and  lower  surfaces  of  the  cerebrum,  dividing  it 
into  several  lobes. 

The  upper  surface  of  the  cerebellum  is  higher  in  the 
middle  than  at  its  edges;  it  is  directed  toward  the  under 
surface  of  the  occipital  lobes  of  the  cerebrum,  and  is  sepa- 
rated from  them  by  the  tentorium  cerehelli.  This  surface 
is  divided  into  two  lateral  hemispheres.  These  are  com- 
pletely separated  in  front  by  a  concavity  which  is  called 
the  incisura  cerehelli  anterior;  this  surrounds  the  posterior 
portion  of  the  corpora  quadrigemina.  Behind,  the  hemi- 
spheres are  separated  by  a  similar  concavity,  which  is  called 
the  incisura  cerehelli  posterior.  In  the  middle  the  hemi- 
spheres are  united  by  an  elevated  mass  which  is  called  the 
median  lobe,  or  the  superior  vermiform  process. 


THE   CEREBELLUM.  379 

The  upper  surface  of  each  cerebellar  hemisphere  is  di- 
vided by  a  transverse  curved  fissure  into  two  lobes,  called 
the  anterior  or  square  lobe  and  the  posterior  or  semilunar 
lobe.  The  anterior  or  square  lobe  is  the  larger;  it  is  the 
portion  anterior  to  the  fissure;  its  inner  border  extends 
backward  to  the  posterior  end  of  the  vermiform  process. 

The  posterior  or  semilunar  lobe  is  narrower  than  the 
former;  it  is  the  portion  posterior  to  the  fissure,  and  is 
limited  behind  and  below  by  the  great  horizontal  fissure. 

The  lower  surface  of  the  cerebellum  is  divided  by  a  wide 
longitudinal  furrow  along  the  median  line  into  two  lateral 
hemispheres.  This  furrow  covers  the  back  part  of  the 
medulla.  The  under  surface  of  each  cerebellar  hemisphere 
rests  in  the  posterior  fossae  of  the  cranium  on  its  side 

This  surface  is  divided  by  several  fissures  into  five  lobes, 
which,  beginning  at  the  front,  are  named  as  follows  : 
1,  the  flocculus;  2,  the  amygdala,  or  tonsil;  3,  the  digastric 
lobe;  4,  the  slender  lobe;  5,  the  posterior  inferior  lobe. 

1.  The  flocculus  is  that  portion  of  the  under  surface 
which  is  situated  anteriorly  and  beneath  the  great  trans- 
verse commissure  or  middle  peduncle  of  the  cerebellum. 

2.  The  amygdala,  or  tonsil,  is  situated  behind  and  inter- 
nally to  the  flocculus;  its  inner  border  forms  part  of  the 
margin  of  the  valley  or  middle  furrow. 

3.  The  digastric  lobe  is  situated  behind  and  externally  to 
the  amygdala,  and  separated  from  it  by  a  curved  fissure. 

4.  The  slender  lobe  is  situated  behind  the  digastric  lobe, 
and  is  separated  from  it  by  another  curved  transverse 
fissure. 

5.  The  inferior  posterior  lobe  is  situated  posteriorly  to 
the  former  lobe,  and  extends  backward  to  the  great  hori- 
zontal fissure  which  separates  it  from  the  superior  poste- 
rior or  semilunar  lobe  of  the  upper  surface  of  the  hemi- 
sphere. 

The  longitudinal  median  furrow  which  divides  the 
under  surface  of  the  cerebellum  into  the  two  hemispheres 


380     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

is  called  the  vaUey;  projecting  from  the  floor  of  it  is  an 
elongated  prominence  which  is  called  the  inferior  vermi- 
form process,  and  consists  of  four  parts,  which,  beginning 
at  the  rear,  are  as  follows:  the  commissura  brevis,  the 
pyramid,  the  uvula,  and  the  nodule. 

H\iQ  commissura  brevis,  or  tuber  ralvulce,  is  a  small,  trans- 
verse band  which  unites  the  inferior,  posterior,  and  the 
slender  lobes  of  the  two  hemispheres. 

The 2)yramicl  is  situated  in  front  of  the  commissura  brevis, 
between  the  two  hemispheres. 

The  uvula  is  the  portion  which  is  placed  between  the 
amygdalae  or  tonsils  of  the  two  hemispheres. 

The  nodule  is  the  anterior  cone-like  termination  of  the 
inferior  vermiform  process;  the  nodule  projects  into  the 
fourth  ventricle.  From  each  side  a  wide  band  passes  out- 
ward to  the  side  of  the  flocculus  on  each  side;  this  is  called 
the  posterior  medullary  velum,  or  the  commissure  of  the 
flocculi. 

The  cerebellum  consists  of  a  layer  of  gray  nerve-sub- 
stance externally  and  white  nerve-substance  internally. 
The  external  gray  covering  is  called  the  cortical  substance; 
the  internal  white  matter  is  called  the  medullary  substance; 
in  the  midst  of  this  is  a  mass  of  gray  substance  which  is 
called  the  corpus  dentatum. 

The  Corticcd  Gray  Matter  of  the  Cerehellnm. 

The  surface  of  the  cerebellum  is  traversed  by  numerous 
transverse  arched  furrows  or  sulci;  these  give  to  the  surface 
a  transversely  striated  and  foliated  appearance.  The  pur- 
pose of  these  sulci  is  the  same  as  that  of  the  sulci  of  the 
cerebrum — viz.,  to  increase  the  surface  without  an  increase 
of  the  cerebellar  surface  itself. 

The  cortical  gray  matter  of  the  cerebellum  consists  of 
laminse  which  extend  outward  from  the  surface  of  the 
medullary  substance,  and  which  are  separated  by  the  sulci 


THE    CEREBELLUM.  381 

on  the  surface  of  the  cortex.  If  examiDed  microscopically 
it  will  be  seen  that  it  consists  of  two  distinct  layers. 

The  outer  layer  is  grayish  in  color;  it  consists  of  neu- 
roglia, of  delicate  connective-tissue  fibres,  of  small  granular 
cells,  and,  lastly,  of  nerve-fibrillae  which  are  continuous 
with  poles  of  certain  cells  in  the  depth  of  this  layer,  and 
pass  outward  at  right  angles.  The  cells  from  which  these 
fibres  arise  are  called  the  corpuscles  of  Purkinje;  they  are 
the  characteristic  cells  of  the  cerebellum.  They  are  oblong 
in  shape  and  give  off  from  their  upper  border  processes 
which  ascend  in  the  upper  layer.  From  their  lower  border 
these  cells  give  off  poles,  or  elongated  processes,  which 
pass  iuward  through  the  inner  layer  and  are  continuous 
with  the  axis-cylinder  of  the  medullated  nerve-fibres  of  the 
medullary  substance. 

The  inner  layer  of  the  cortex  is  of  a  reddish  color;  it  is 
composed  of  numerous  small,  granular,  nucleated  cells; 
they  are  stellate  in  form  and  give  off  delicate  processes 
which  form  a  fine  reticulum  between  the  cells;  the  whole 
is  embedded  in  a  matrix  of  gelatinous  material. 

The  Medullary  Substance  of  the  Cerebellum. 

The  medulla  of  the  cerebellum  presents,  on  a  transverse 
section  of  the  organ,  the  shape  of  a  tree  consisting  of  a 
stem  and  many  rami;  this  peculiar  arrangement  is  called 
the  arbor  vitoe. 

The  medullary  substance  consists  of  medullated  nerve- 
fibres,  which,  according  to  their  arrangement,  are  divided 
into  (1)  the  commissural  fibres,  (2)  the  arcuate  or  associ- 
ation fibres,  (3)  the  peduncular  fibres. 

1.  The  commissural  fibres  are  those  which  pass  trans- 
versely through  the  anterior  and  posterior  part  of  the 
vermiform  process  connectiug  the  two  hemispheres. 

2.  The  arcuate  or  association  fibres  are  those  which  pass 
around  the  bottom  of  the  sulci  and  connect  the  laminae  of 
the  cortical  substance  of  each  hemisphere. 


382     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

3.  The  j^echincuhir  ^hres  are  those  which  are  continued 
into  the  peduncles  of  the  cerebellum. 

The  Peel  uncles  of  the  Cerebellum. 

The  cerebellum  is  connected  with  the  other  parts  of  the 
brain  by  bands  of  nerve-fibres  which  are  called  its  pedun- 
cles—three on  each  side,  called  the  superior,  middle,  and 
inferior  peduncles. 

The  superior  peduncles  are  two  round  bands,  one  on  each 
side,  which  connect  the  cerebellum  with  the  corpora 
quadrigemina  of  the  cerebrum  in  front. 

The  superior  peduncle,  or  processus  e  cerehello  ad  testes, 
consists  of  nerve-fibres  which  arise  from  the  optic  thala- 
mus on  its  side  ;  these  pass  forward  to  the  upper  surface 
of  the  crura  cerebri,  and  finally  emerge  as  a  round  band 
from  beneath  the  posterior  border  of  the  testes  of  the  cor- 
pora quadrigemina.  As  the  two  peduncles  emerge  they  pass 
backward  and  diverge  to  enter  the  hemispheres  of  the 
cerebellum ;  in  these,  most  of  the  fibres  of  each  peduncle 
enter  the  corpus  dentatum,  and  some  of  these  pass  to  the 
cortical  substance  of  the  under  portion  of  the  cerebellum. 

Some  of  the  fibres  of  the  superior  peduiicles  decussate 
beneath  the  corpora  quadrigemina,  so  that  each  peduncle 
as  it  emerges  from  the  testes  contains  fibres  from  the  optic 
thalami  on  both  sides.  As  the  superior  peduncles  pass 
backward  and  diverge  they  form  the  upper  part  of  the 
lateral  boundary  of  the  fourth  ventricle.  Above,  the  supe- 
rior peduncles  are  connected  by  a  thin  transverse  lamella 
of  wdiite  substance  which  is  called  the  valve  of  Vieussens 
and  forms  a  part  of  the  roof  of  the  fourth  ventricle  ;  it  is 
connected  in  front  with  the  posterior  border  of  the  testes,. 
and  behind  with  the  anterior  end  of  the  vermiform  process. 

The  middle  peduncles,  or  crura  of  the  cerebellum,  also 
called  the  j^rocessus  ad  pontem,  are  two  thick  bands  of 
nerve-fibres  which  arise  from  the  cells  of  the  cortical  gray 
substance  of  the  cerebellar  hemispheres,  and  then  curve  for- 
ward to  the  pons  Varolii,  forming  its  deep  transverse  fibres. 


THE   CEREBELLUM.  383 

The  infeiHor  pecluncles  connect  the  cerebellum  with  the 
medulla  oblongata. 

The  inferior  peduncle,  or  j^rocessus  ad  medullam  on  each 
side,  consists  of  continuous  fibres  of  the  restiform.  body  on 
that  side  of  the  medulla.  As  the  peduncles  pass  upward 
they  diverge  and  form  the  inferior  part  of  the  lateral  boun- 
daries of  the  fourth  ventricle.  The  fibres  of  the  inferior 
peduncles  enter  the  cerebellar  hemispheres  and  pass  to 
the  cortical  gray  substance  in  their  upper  part. 

Tlie  Central  Gray  Mass  or  Ganglion  of  the  Cerebellum. 

The  corjnts  dentatum,  or  ganglion  of  the  cerebellum,  is 
located  near  the  centre  of  the  medullary  substance  ;  it 
consists  of  a  capsule  of  gray  substance  which  has  a  ser- 
rated surface;  from  the  interior  of  the  capsule  nerve-fibres 
emerge  which  pass  outward  in  the  superior  peduncles  of 
the  cerebellum. 

Situated  at  the  anterior  end  or  point  of  the  vermiform 
process  are  two  microscopical  masses  of  gray  substance; 
they  are  called  the  roof  nuclei  of  Stilling  and  project  into 
the  roof  of  the  fourth  ventricle. 

TJie  Functions  of  the  Cerebellwn . 

The  cerebellum  is  the  organ  which  governs  the  harmony 
and  co-ordination  of  the  voluntary  movements  ;  it  is  also 
the  organ  for  the  sense  of  body  equilibrium. 

Eemoval  of  parts  or  the  whole  of  the  cerebellum  is  not 
followed  by  a  loss  of  sensation  or  any  of  the  special  senses, 
nor  by  a  paralysis  of  any  muscles  ;  the  cerebellum  is 
therefore  not  an  organ  of  motion  or  of  sensation. 

When  the  cerebellum  of  an  animal  is  removed  it  is  no 
longer  capable  of  maintaining  the  equilibrium  of  its  body; 
its  motions  become  weakened  and  disorderly,  the  animal 
assumes  a  staggering,  unsteady  gait,  it  often  moves  back- 
ward instead  of  'forward,  and  it  has  a  tendency  to  fall 
backward. 


384     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

Removal  of  one  lateral  half  is  followed  by  motor  dis- 
turbances on  one  side  of  the  body.  These  disturbances 
have  the  character  ol  forced  niovements ;  the  animal  makes 
peculiar  jerky,  convulsive  motions,  and  has  a  tendency  to 
fall  to  one  side  and  to  roll  continuously  sideways,  always 
rolling  toward  the  side  from  which  the  cerebellar  half  is  re- 
moved. 

These  experiments  and  observations,  and  the  anatomical 
relations  of  the  cerebellum  to  the  other  parts  of  the  brain, 
tend  to  show  that  the  efferent  fibres  arising  from  the  cells 
of  gray  substance  of  the  cerebellum  conduct  impulses 
which  influence  the  motor  impulses  which  arise  from  the 
other  organs  of  the  brain. 

THE   PONS   VAROLII. 

Its  Anatomy  ayid  Structure. 

The  pons  is  that  portion  of  the  brain  which  connects  its 
various  parts;  it  is  situated  below  the  crura  cerebri,  in 
front  of  the  cerebellum,  and  above  the  medulla  oblongata. 

The  pons  consists  of  an  anterior  and  a  posterior  part. 

The  anterior  part  is  composed  of  transverse  and  longi- 
tudinal fibres,  and,  interposed  between  these,  smaller 
masses  of  gray  matter. 

The  anterior  surface  consists  of  a  superficial  layer  of 
transverse  fibres,  which  laterally  are  continued  outward 
and  backward  and  form  the  middle  peduncles  of  the  cere- 
bellum. Above  this  superficial  layer  there  is  a  mass  of 
longitudinal  fibres;  these  are  continuous  with  the  fibres 
of  the  pyramids  of  the  medulla,  and  are  continued  upward 
as  the  fibres  of  the  crusta  or  superficial  layer  of  the  crura 
cerebri.  Above  this  layer  of  longitudinal  fibres  is  a  third, 
the  deep  transverse  layer;  its  fibres  pass  out  laterally  and 
form,  with  the  superficial  transverse  fibres,  the  middle 
peduncles  of  the  cerebellum. 

In  the  layer  of  the  deep  transverse  fibres  are  numerous 
collections  of  nerve-cells  which  are  connected  with  some  of 


THE   CEREBELLUM.  385 

the  fibres  of  this  layer.  There  is  also  located,  near  the 
lower  end,  a  collection  of  gray  matter  which  is  called  the 
superior  olivary  yiucleus ;  it  is  covered  with  transverse 
fibres  which  are  called  the  trapezium;  these  fibres  are 
probably  connected  with  the  cells  of  the  olivary  nucleus. 

The  anterior  surfa.ce  of  the  pons  presents  a  striated 
appearance,  which  is  produced  by  the  superficial  trans- 
verse fibres;  anteriorly  this  surface  is  marked  by  a  well- 
defined  border  from  which  the  crura  cerebri  emerge. 

The  upper  portion  of  the  pons  is  composed  of  the  con- 
tinuation of  the  formatio  reticularis  of  the  medulla  ob- 
longata. 

The  posterior  surface  of  the  pons  forms  part  of  the  floor 
of  the  fourth  ventricle.  The  structure  of  this  surface 
contains  several  collections  of  nerve-cells,  which  are  the 
deep  origin  of  some  of  the  cranial  nerves. 

These  nuclei  are  arranged  in  pairs — one  pair  from  which 
the  sensory  roots  of  the  fifth  nerves  arise;  a  second  pair 
from  which  the  motor  roots  of  the  same  nerves  arise;  a 
third  pair  are  the  deep  origin  of  the  sixth  pair  of  cranial 
nerves  ;  a  fourth  pair  from  which  the  facial  or  seventh 
nerves  arise  ;  and  a  fifth  pair  from  which  the  eighth 
cranial  or  auditory  nerves  arise.  This  last  pair  is  situated 
at  the  junction  of  the  pons  with  the  medulla. 

The  Functions  of  the  Pons  Varolii. 

The  pons  is  an  organ  of  conduction.  Through  its  va- 
rious fibres  impressions  are  conducted  to  and  from  the 
various  parts  of  the  brain  and  the  medulla  oblongata  and 
spinal  cord.  Section  Or  destruction  of  parts  of  the  pons 
produces  sensory  and  motorial  disturbances — viz.,  anaes- 
thesia and  paralysis. 

The  function  of  the  pons  as  a  nerve-centre  is  not  known. 
The  physiology  of  the  various  nuclei  on  the  posterior  sur- 
face of  the  pons  I  will  consider  later  in  connection  with 
the  physiology  of  the  cranial  nerves. 
25 


LECTURE   XLI. 

THE   MEDULLA   OBLONGATA. 

Its  Anatomy  and  Structure. 

The  medulla  oblongata  is  that  portion  of  the  cerebro- 
spinal axis  which  connects  the  spinal  cord  with  the  brain. 

The  medulla  is  pyramidal  in  form,  and  directed  with  its 
base  forward  and  upward  and  with  its  apex  backward  and 
downward.  Its  anterior  surface  rests  on  the  basilar  pro- 
cess of  the  occipital  bone,  and  its  posterior  surface  is  cov- 
ered by  the  valley  or  groove  which  separates  the  two  cere- 
bral hemispheres;  the  anterior  part  of  the  posterior  surface 
of  the  medulla  forms  a  part  of  the  floor  of  the  -fourth  ven- 
tricle. The  medulla  is  about  1  inch  long,  three-quarters  of 
an  inch  wide,  and  half  an  inch  thick  at  its  base,  and  thin- 
ner and  round  toward  the  apex. 

The  medulla  oblongata  is  divided  into  symmetrical  late- 
ral halves  by  an  anterior  and  a  posterior  median  fissure 
which  runs  along  the  middle  line  of  its  anterior  and  poste- 
rior surface,  and  which  is  continuous  below  with  the  cor- 
responding fissure  of  the  spinal  cord. 

The  anterior  median  fissure  is  interrupted  below  by  the 
decussation  of  the  fibres  of  the  pyramids. 

ThQ  posterior  median  fissure  expands  at  about  the  middle 
of  the  posterior  surface,  the  space  between  its  sides  form- 
ing the  posterior  part  of  the  floor  of  the  fourth  ventricle. 

Each  lateral  half  of  the  medulla  is  divided  by  shallow 
longitudinal  furrows,  from  which  some  of  the  cranial  nerves 
arise,  into  several  columns  which  are  continuous  with  the 
columns  of  the  spinal  cord. 


THE  MEDULLA  OBLONGATA.  387 

That  portion  which  is  situated  between  the  anterior  me- 
dian fissure  and  the  furrow  from  which  the  several  fila- 
ments  of  the  liypoglossal  neiwe  arise  is  called  the  anterior 
pyramid:  it  is  continuous  with  the  anterior  column  of  the 
cord.  That  portion  which  is  situated  between  the  furrow 
from  which  the  filaments  of  the  hypoglossal  nerve  arise, 
and  that  from  w^ich  the  fibres  of  the  glosso -pharyngeal, 
the  pneumogastric,  and  the  spinal  accessory  nerves  arise, 
is  continuous  with  the  lateral  column  of  the  cord.  In  the 
lower  part  of  the  medulla  this  portion  is  called  the  lateral 
tract;  in  the  upper  part  of  the  medulla  an  oval  mass,  called 
the  olivary  body,  protrudes  between  the  anterior  pyramid 
and  the  lateral  tract. 

That  portion  of  the  medulla  w^hich  is  continuous  with 
the  posterior  column  of  the  cord  is  situated  between  the 
furrow  from  w-hich  the  fibres  of  the  glosso-pharyngeal,  the 
pneumogastric,  and  the  spinal  accessory  nerves  arise,  and 
the  posterior  median  fissure.  This  segment  of  the  medulla 
is  divided  by  several  shallow  longitudinal  grooves  into 
minor  columns.  In  the  lower  part  of  the  medulla  these  are 
called,  from  the  posterior  median  fissure  outward,  ihefuni- 
culus  gracilis,  the  funiculus  cuneatus,  aud  the  funiculus 
of  Rolando.  In  the  upper  portion  of  the  medulla  the  funi- 
culus cuneatus  and  the  funiculus  of  Eolando  join  and  form 
the  restiform  body. 

The  pyramid  or  anterior  column  on  the  surface  of  the 
medulla,  on  each  side  of  the  anterior  median  fissure,  con- 
sists of  two  bundles  of  longitudinal  fibres.  The  outer  por- 
tion of  these  fibres  is  continuous  with  the  fibres  from  the 
direct  pyramidal  tract  of  the  anterior  column  of  the  spinal 
cord  on  the  same  side;  the  inner  portion  of  these  fibres  is 
continuous  with  the  fibres  which  are  seen  to  decussate 
across  the  anterior  median  fissure  in  its  lower  part.  These 
fibres  are  derived  from  the  crossed  pjyramidal  tract  of  the 
latercd  column  on  the  other  side  of  the  cord. 

The   fibres  of  the  pyramids  ascend  as  the   longitudinal 


388     LECTURES   ON    HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

fibres  of  the  pons  Varolii,  and  they  are  continued  upward 
and  forward  as  the  fibres  of  the  superficial  portion  or  the 
crusta  of  the  crura  cerebri;  they  finally  enter  the  cerebral 
hemispheres,  some  passing  through  the  internal  capsule 
directly  to  the  cortical  substance,  and  some  through  the 
corpus  striatum.  Above,  the  anterior  pyramid  is  separated 
from  the  olivary  body  by  a  furrow. 

The  lateral  tract  of  the  medulla  consists  of  fibres  arranged 
in  three  sets;  they  are  continuous  with  the  fibres  of  the 
several  fasciculi  of  the  lateral  column  of  the  spinal  cord. 

The  three  sets  of  fibres  of  the  lateral  tract  of  the  medulla 
are: 

1.  The  lateral  cerebellar  set  are  continuous  with  the  fibres 
of  the  cerebellar  column  of  the  lateral  column  of  the  cord 
on  the  same  side;  the  fibres  ascend  and  pass  backward  to 
join  the  fibres  of  the  restiform  body  of  the  posterior  seg- 
ment of  the  medulla;  in  the  restiform  body  these  fibres  pass 
backward,  forming  the  inferior  peduncle  of  the  cerebellum 
on  one  side. 

2.  The  crossed  ptjramidal  set.  Its  fibres  are  continuous 
with  those  of  the  crossed  pyramidal  fasciculus  of  the  cord 
below  on  the  same  side.  In  the  medulla  these  fibres  ascend 
for  a  short  distance,  then  pass  transversely  behind  the 
pyramid  on  the  same  side,  and,  decussating  across  the  me- 
dian fissure,  join  the  fibres  of  the  pyramid  on  the  opposite 
side. 

3.  This  set  consists  of  the  fibres  of  the  anterior  radicidar 
zone  and  the  mixed  Icdercd  column  of  the  lateral  column  of 
the  cord  on  the  same  side.  In  the  medulla  these  fibres 
ascend  in  the  format io  reticularis,  to  be  described  later. 

The  posterior  segment  or  column  of  the  medulla  consists, 
in  the  lower  part,  of  several  minor  columns. 

The  funiculus  gracilis  is  that  column  of  the  posterior 
segment  of  the  medulla  which  is  placed  beside  the  poste- 
rior median  fissure;  its  fibres  are  continued  from  those  of  the 
column  of  Goll  or  the  posterior  median  column  of  the  cord. 


THE  MEDULLA  OBLONGATA.  389 

The  funiculus  cuneatus  is  that  colamn  of  the  posterior 
segment  which  is  placed  externally  to  the  fnniculus  graci-' 
lis.  The  fibres  of  the  funiculus  cuneatus  are  continuous 
with  the  fibres  of  the  funiculus  cuneatus  of  the  posterior 
colurou  of  the  cord. 

ThQ  funiculus  of  Rolando  is  that  column  which  is  located 
externally  to  the  funiculus  cuneatus. 

The  funiculus  of  Rolando  is  an  elongated  prominence  or 
elevation  in  the  lower  part  of  the  posterior  segment  of  the 
medulla,  produced  b)^  the  enlargement  of  the  head  of  the 
posterior  horn  of  gray  matter  in  this  part  of  the  medulla. 
This  enlargement  is  covered  with  a  layer  of  longitudinal 
fibres  which  are  continuous  from  below  with  some  of  the 
fibres  of  the  funiculus  cuneatus  of  the  spinal  cord. 

The  fibres  of  the  funiculus  of  Rolando,  and  those  of  the 
funiculus  gracilis  of  the  posterior  segment  of  the  medulla, 
join  together  in  the  upper  part  of  this  segment,  forming  a 
column  which  is  called  the  restiform  body;  in  this  they 
pass  outward  and  upward  to  form  the  inferior  peduncle  of 
the  cerebellum  on  its  side.  Some  fibres  of  the  funiculus 
cuneatus  probably  terminate  in  a  collection  of  gray  matter 
which  is  called  the  nucleus  cuneatus  ;  this  is  located  in  the 
upper  portion  of  the  substance  of  the  funiculus  cuneatus, 
causing  a  rounded  prominence  on  its  surface  at  that  point. 

The  fibres  of  the  funiculus  gracilis  do  not  pass  up  to  the 
restiform  body,  but  terminate  in  a  mass  of  gray  substance 
which  is  placed  in  the  substance  of  the  funiculus  in  its 
upper  portion.  This  gray  mass  is  called  the  nucleus  graci- 
lis; it  produces  a  round  prominence  on  the  outer  surface  of 
this  funiculus. 

The  olivary  body  is  an  oval-shaped  body  which  consists 
externally  of  white  matter,  and  internally  of  gray  sub- 
stance in  the  form  of  a  dentated  capsule;  this  capsule  is 
called  the  corpus  dentatum  of  the  medulla.  The  olivary 
body  is  situated  on  the  anterior  aspect  of  the  upper  part  of 
the  medulla,  between  the  anterior  pyramid  and  the  resti- 


390     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

form  body.  It  is  placed  somewhat  behind  the  pyramid, 
and  separated  from  it  by  a  groove  from  which  the  fibres  of 
the  hypoglossal  nerve  arise;  from  the  restiform  bodies  it 
is  separated  by  a  groove  from  which  the  pneumogastric, 
hypoglossal,  and  the  spinal  accessory  nerves  arise. 

From  the  anterior  median  fissure  in  the  upper  part  of 
the  medulla  are  seen  to  emerge  a  set  of  fibres  w^hich  arch 
over  the  pyramid  and  over  the  under  part  of  the  olivary 
body  on  each  side,  and  then  enter  the  restiform  body ;  these 
are  called  the  superficial  arcuate  or  arc i form  fibres. 

The  Structure  of  the  Medulla. 

The  medulla  oblongata  consists  of  tvhite  matter  exter- 
nally and  gray  matter  internally.  If  a  transverse  section 
of  the  medulla  is  made,  it  will  be  seen  that  the  surface  of 
this  section  is  divided  into  three  wedge-shaped  areas  or 
segments  by  the  various  cranial  nerves,  which  from  their 
.nuclei  pass  horizontally  outward  to  emerge  from  the  shal- 
low grooves,  on  the  outer  surface  of  the  medulla,  w^hich 
divide  it  into  the  several  columns  above  mentioned.  These 
three  areas  are  called  the  anterior,  posterior,  and  lateral 
area.  The  anterior  area  is  the  portion  between  the  median 
fissure  and  the  hypoglossal  nerve,  which,  from  its  nucleus 
in  the  rear  of  the  medulla,  passes  horizontally  outward  and 
forward  through  the  substance  of  the  medulla,  and  w^hich 
finally  emerges  from  the  shallow  groove  on  the  surface  of 
the  medulla  which  separates  the  anterior  pyramid  in  front 
from  the  lateral  segment.  The  lateral  area  is  the  portion 
between  the  hypoglossal  nerve  as  it  passes  horizontally 
forward  and  outward  from  its  nucleus,  and  the  pneumo- 
gastric nerve,  which  from  its  nucleus  passes  horizontally 
outward  to  emerge  from  the  furrow  which,  on  the  surface 
of  the  medulla,  separates  the  lateral  segment  from  the 
posterior  segment. 

The  posterior  area  is  the  portion  posterior  to  the  hori- 
zontally passing  outward  pneumogastric  nerve;  this  portion 


THE  MEDULLA  OBLONGATA.  391 

is  separated  from  the  same  area  on  the  other  side  of  the 
medulla  by  the  posterior  median  fissure  on  the  outer  sur- 
face of  the  medulla;  this  area  corresponds  to  the  portion 
which,  by  several  shallow  longitudinal  fissures,  is  divided 
into  the  several  minor  columns  above  mentioned. 

The  peripheral  portion  of  these  three  areas  is  composed 
of  the  fibres  which  form  the  various  columns  into  which 
the  surface  of  the  medulla  is  divided.  The  inner  portion  of 
these  areas  is  composed  of  a  reticulated  structure  of  nerve- 
fibres  which  is  called  the  formatio  reticularis ;  this  struc- 
ture consists  of  longitudinal  and  transverse  fibres. 

The  longitudinal  fibres  are: 

1.  The  fibres  of  the  fundamental  fasciculus  of  the  anterior 
column  of  the  cord. 

2.  The  fibres  from  the  mixed  lateral  column  and  from 
the  anterior  radicular  zone  of  the  lateral  column  of  the 
cord. 

3.  Fibres  arising  from  the  capsule  or  interior  of  the  corpus 
dentatum  of  the  olivary  body  of  the  medulla. 

4.  The  fibres  from  the  funiculus  cuneatus  and  from  the 
funiculus  gracilis  which  pass  to  their  respective  nuclei. 

The  transverse  fibres  of  the  formatio  reticularis  are  the 
deep  arcuate  or  arciform  fibres.  These  fibres  are  very 
abundant.  Some  of  them  join  the  superficial  arciform ;  some 
pass  to  the  raphe  in  the  anterior  median  fissure,  which  is 
formed  by  the  meeting  of  the  superficial  arciform  fibres 
from  both  sides  of  the  medulla.  These  fibres  arise  from 
ganglion  cells  in  the  depth  of  the  anterior  median  fissure; 
from  these  cells  also  arise  some  of  the  deep  arciform  fibres; 
some  of  these  pass  into  the  restiform  bodies.  Most  of  the 
fibres  of  the  formatio  reticularis  are  continued  upward 
and  forward  in  the  upper  layer  or  tegmentum  of  the  crura 
cerebri;  in  the  cerebral  hemispheres  the  fibres  of  the  teg- 
mentum pass  up  to  the  optic  thalami. 

The  fibres  of  the  formatio  reticularis  and  those  of  the 
columns  constitute  the  white  substance  of  the  medulla. 


392     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

The  Gray  Substance  of  the  Medulla. 

In  the  lower  part  of  the  medulla  the  gray  substance  is 
continuous  with  that  of  the  spinal  cord.  On  transverse 
section  of  the  lower  part  of  the  medulla  it  presents  the 
same  arrangement  as  in  the  cord — namely,  each  lateral  half 
of  the  medulla  contains  a  crescentic  mass  directed  with  its 
concavity  outward,  and  having  an  anterior  horn  which 
passes  outward,  and  a  posterioi  horn  which  passes  back- 
ward into  the  substance  of  the  medulla. 

In  the  upper  part  of  the  medulla  the  gray  matter  is  more 
abundant  and  not  arranged  with  such  regularity  as  in  the 
lower  part.  At  the  point  on  the  posterior  surface  of  the 
medulla  where  the  funiculi  graciles  and  the  restiform 
bodies  diverge  as  they  pass  upward  to  form  the  posterior 
lateral  boundary  of  the  fourth  ventricle,  the  gray  matter 
is  exposed.  The  point  where  the  posterior  median  fissure 
separates  is  termed  the  calamus  scriptorius.  At  this  the 
central  canal  of  the  gray  matter  expands  and  the  gray 
matter  spreads,  forming  the  covering  of  the  floor  of  the 
fourth  ventricle;  in  it  are  seen  prominences  which  are 
caused  by  a  collection  of  cells  which  are  the  nuclei  for 
several  of  the  cranial  nerves. 

The  gray  mass  of  the  horns  of  the  crescentic  masses  is 
separated  into  several  masses  or  nuclei  by  the  fibres  of  the 
white  substance  of  the  medulla;  in  these  regions  these 
masses  are  pushed  outward  toward  the  columns  on  the 
surface  of  the  medulla  and  toward  the  floor  of  the  fourth 
ventricle. 

The  head  of  the  anterior  hoi'ii  is  separated  from  the  main 
mass  by  fibres  of  the  crossed  pyramidal  tract  of  the  cord. 
As  they  decussate  in  the  medulla  this  mass  is  pushed  out- 
ward toward  the  lateral  tract,  and  constitutes  the  lateral 
nucleus  which  is  situated  beneath  the  surface  of  this  tract. 

The  other  portion  of  the  anterior  horn  is  also  separated 
into  several  masses  by  the  fibres  of  the  formatio  reticularis; 
one  of  these  masses  is  pushed  toward  the  floor  of  the  fourth 


THE  MEDULLA  OBLOXGATA.  393 

ventricle,  producing  in  it  an  elevation;  this  mass  is  known 
as  the  nucleus  tei^es.  From  a  group  of  nerve  cells  arise  the 
fibres  of  the  hypoglossal  nerve. 

The  head  of  the  posterior  horn  is  separated  from  the 
main  mass;  it  enlarges  and  is  pushed  outward,  formiug  a 
separate  mass  which  is  situated  near  the  surface  of  the 
lateral  tract,  causing  the  protrusion  of  the  funiculus  of  Ro- 
lando on  the  outer  surface  of  the  medulla  posteriorly. 

The  main  portioD  of  the  posterior  horn  is  divided  into 
two  separate  masses  which  are  called  the  nucleus  gracilis  and 
the  nucleus  cuneatus  ;  these  are  situated  beneath  the  surface 
of  the  funiculus  gracilis  and  the  funiculus  cuneatus.  An- 
other separate  mass  from  the  posterior  horn  is  pushed 
toward  the  floor  of  the  fourth  ventricle,  producing  in  it  an 
elevation  which  is  called  the  ala  cinerea.  This  is  situated 
externally  to  the  elevation  produced  by  the  nucleus  teres  ; 
from  it  arise  the  roots  of  the  pneumogastric,  the  glosso- 
pharyngeal, and  the  accessory  branch  of  the  spinal  acces- 
sory nerve.  Externally  to  the  ala  cinerea  is  located  a  mass 
of  ganglion  cells  from  which  the  main  portion  of  the  audi- 
tory nerve  arises.  In  the  substance  of  the  medulla  there  is 
another  separate  mass — viz.,  the  corpus  dentatuni  of  the 
olivary  body. 

Tlie  Functions  of  the  Medulla  Oblongata. 

The  medulla  conducts  impulses  from  the  spinal  cord  to 
the  brain,  and  vice  versa,  and  also  impulses  which  ori- 
ginate in  the  various  centres  in  the  medulla.  The  medulla 
also  transfers  impulses.  But  it  is  not  only  an  organ  for 
the  conduction  and  transference  of  impulses  ;  it  is  also 
the  seat  of  the  centres  of  many  important  functions,  such 
as  respiration,  etc.  The  brain  and  portions  of  the  spinal 
cord  may  be  injured  or  removed  and  life  may  still  con- 
tinue for  some  time.  But  injury  to  the  medulla,  especially 
in  its  middle  part,  often  causes  instantaneous  death,  owing 
to  the  destruction  of  the  respiratory  and  cardiac  centres. 


394     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  activity  of  the  various  nerve-centres  in  the  medulla 
may  be  automatic  or  reflex.  The  normal  activity  of  these 
centres  depends  upon  the  proper  exchange  of  the  gases  of 
the  blood. 

The  automatic  centres  in  the  medulla  are  : 

1.  The  centre  of  respiration. 

2.  The  cardio- inhibitory  centre. 

3.  Tiie  cardio-accelerating  centre. 

4.  Tlie  vasomotor  centre. 

5.  The  vasodilator  centre. 

6.  The  sweat  centre. 

The  centre  of  respiration  is  located  in  the  gray  matter  of 
the  floor  of  the  fourth  ventricle,  between  the  origin  of  the 
pneumogastric  and  spinal  accessory  nerves.  The  centrum 
is  double-sided;  wiien  divided  longitudinally  the  respira- 
tory movements  will  continue  symmetrically  on  both  sides, 
but  if  one  lateral  half  of  the  centre  is  destroyed  the  respira- 
tory movements  will  cease  on  that  side  of  the  body.  The 
centre  of  respiration  consists,  on  each  side,  of  two  parts — 
one  which  influences  the  inspiratory,  and  one  the  expira- 
tory movements.  The  respiratory  centre  is  automatic 
and  by  its  rhythmical  activity  presides  over  the  regularity 
and  rhythm  of  the  respiratory  motions.  The  activity  of 
the  centre  may  also  be  influenced  by  reflex  impressions 
conveyed  to  it  through  centripetal  nerves.  It  has  been 
observed  that  the  pulmonary  branches  of  the  pneumo- 
gastric conduct  accelerating  impressions  to  the  centre  of 
respiration.  Section  of  these  causes  a  decrease  of  the 
respiratory  movements.  Nerves  conducting  accelerating 
impressions  to  the  centre  of  respiration  are  also  contained 
in  the  nerves  of  the  skin  and  in  the  sensory  nerves  of  the 
eye  and  ear. 

Inhibitory  impulses  are  conducted  to  the  centre  in  fibres 
of  the  superior  and  inferior  laryngeal  branches. 

The  respiratory  motions  are  also,  to  a  certain  extent, 
under  the  control  of  the  will. 


THE  MEDULLA  OBLONGATA.  395 

The  irritability  and  activity  of  the  respiratory  centre 
depend  upon  the  quantity  of  0  and  C0„  in  the  blood. 
An  excess  of  0  and  diminution  of  CO,  decreases  or  totally 
interrupts  the  irritability  and  activity  of  the  centre,  pro- 
ducing the  condition  known  as  apnoea. 

An  increase  of  the  CO,  and  decrease  of  O  in  the  blood 
produces  dysjjnoea,  characterized  by  rapid  and  labored  res- 
piratory motions  and  deep  respirations. 

Experiments  have  shown  that  in  the  cerebral  hemi- 
spheres, and  also  in  the  spinal  cord,  there  are  situated 
respiratory  centres,  which,  however,  are  subordinate  to, 
and  controlled  by,  the  centre  in  the  medulla. 

The  cardio-inliihitory  centre  is  located  near  the  restiform 
body;  it  is  an  automatic  centre.  Its  irritability  and  its 
activity  are  influenced,  like  those  of  the  respiratory  centre, 
by  the  cpantity  of  0  and  CO,  in  the  blood. 

The  activity  of  this  centre  may  also  be  influenced  by 
reflex  impressions  received  through  centripetal  nerves. 
The  centre  may  be  irritated  by  irritation  of  the  vagus  and 
of  the  cervical  and  abdominal  sympathetic  nerves.  For 
example,  a  blow  against  the  abdomen  may  cause  death  by 
irritation  of  the  sensory  nerves  of  the  abdominal  viscera 
and  the  resulting  reflex  irritation  of  the  cardio-inhibitoiy 
centre. 

The  activity  of  this  centre  is  decreased  by  filling  the 
lungs  with  air,  as  shown  by  the  rapid  cardiac  motions 
when  this  is  done.     This  is  due  to  reflex  action. 

The  cardio-accelercding  centre  sends  accelerating  im- 
pulses to  the  cardiac  plexus  through  fibres  of  the  sympa- 
thetic nerve. 

The  vasomotor  cerdre  is  located  in  the  upper  part  of  the 
floor  of  the  fourth  ventricle.  From  it  motorial  impulses 
are  conducted  to  the  muscles  of  the  arteries.  The  activity 
of  this  centre  may  be  influenced  by  reflex  irritation. 

A  vasodilcdor  centre  in  the  medulla  has  not  as  yet  been  de- 
monstrated, but  it  is  very  probable  that  such  a  centre  exists. 


390     LECTURES   ON   HUMAN  PHYSIOLOGY   AND    HISTOLOGY. 

The  sweat-centre  in  the  medulla  predominates  over  the 
sweat- centres  in  the  spinal  cord.  This  centre  in  the 
medulla  is  double-sided;  its  irritation  produces  sweating 
of  the  whole  surface  of  the  body. 

In  the  medulla  oblongata  there  are  certain  special 
centres,  such  as  a  diabetic  centre,  an  irritation  of  which 
produces  diabetes  ;  a  centre  the  irritation  of  which  causes 
convulsions,  etc.  These  centres  are  not  in  a  constant 
tonic,  active  state. 

The  Reflex  Centres  in  the  Medulla  Oblonyata. 

In  the  medulla  oblongata  there  are  found  a  series  of 
nerve-centres  which  are  purely  reflex ;  their  activity  is 
excited  ordinai'ily  by  impressions  received  through  centri- 
petal nerves.     These  centres  are: 

1.  A  centre  for  the  closure  of  the  eyelids. 

2.  A  centre  for  the  act  of  sneezing. 

3.  A  centre  for  deglutition. 

4.  A  centre  for  mastication. 

5.  A  centre  for  salivary  secretion. 

6.  A  centre  for  the  act  of  vomiting. 

7.  A  centre  for  the  act  of  coughing. 

8.  A  centre  for  the  dilatation  of  the  pupils. 

9.  A  centre  which  controls  all  other  reflex  centres  in  the 
medulla. 

In  the  description  of  those  functions  over  which  these 
various  reflex  centres  in  the  medulla  preside,  I  included 
their  neiwous  mechanism  and  mentioned  the  centripetal 
(or  sensory),  the  centrifugal  (or  motor)  nerves,  and  the 
location  of  the  centre  concerned  in  the  various  functions. 

The  various  reflex  centres  in  the  medulla  ordinarily  re- 
ceive the  impulse  for  their  activity  through  a  sensory 
nerve,  but  this  activity  may  also  be  excited  by  direct 
stimulation,  and  their  activity  is  also  influenced  by  the 
quantity  of  the  gases — viz.,  the  oxygen  and  CO^ — in  the 
blood. 


THE  FOURTH  VENTRICLE.  397 


THE  FOURTH  VENTRICLE. 


Before  finishing  the  description  of  the  anatomy  and 
structure  of  the  brain,  I  must  describe  the  narrow,  dia- 
mond shaped  space  which  is  known  as  the  fourth  ventricle 
of  the  brain.  It  is  the  space  between  the  pons  and  medul- 
la below  and  the  cerebellum  above;  it  is  also  called  the 
ventricle  of  the  cerebellum.  At  its  upper  angle  it  com- 
municates above  with  the  third  ventricle  through  the 
aqueduct  of  Sylvius,  and  below  with  the  central  canal  of 
the  spinal  cord. 

The  boundaries  of  the  fourth  ventricle  are  as  follows  : 

lis  floor  is  formed  by  the  posterior  surface  of  the  pons 
Varolii  and  the  medulla  oblongata.  Along  the  middle  line 
of  the  floor,  running  longitudinally,  is  a  fissure  which  ter- 
minates below  at  the  angle  formed  by  the  divergence  of 
the  funiculi  graciles  and  the  restiform  bodies,  and  by  the 
expansion  of  the  central  canal.  This  angle  with  the  fis- 
sure in  its  centre  is  called,  from  its  resemblance  to  the 
point  of  a  pen,  the  calamus  scriptorius.  At  each  side  of 
the  central  fissure  there  is  an  elongated  elevation,  the 
fasciculus  teres ;  this  is  produced  by  a  portion  separated 
from  the  anterior  horn.  Passing  transversely  across  the 
widest  part  of  the  ventricle  are  the  auditory  strice—seYe- 
ral  white  fibres  which  pass  toward  the  origin  of  the  audi- 
tory nerves.  Below  and  above  these  striae  on  each  side 
are  shallow  depressions,  called  the  fovea,  superior  and  in- 
ferior. External  to  the  fasciculus  teres  on  each  side 
there  is  another  minor  elevation,  called  the  ala  cinerea ; 
this  is  produced  by  the  projection  of  a  separate  portion 
from  the  posterior  horns. 

The  gray  matter  which  covers  the  floor  of  the  fourth 
ventricle  presents  several  small  elevated  points  which  are 
the  nuclei  for  the  deep  origin  of  several  cranial  nerves. 

The  following  cranial  nerves  have  their  deep  origin  in 
the  floor  of  the  fourth  ventricle: 


398      LECTURES   ON   HUMAX   PHYSIOLOGY   AND   HISTOLOGY. 

The  sixth  or  abducenf  nerve  arises  from  a  nucleus  which 
is  located  near  the  upper  part  of  the  fasciculus  teres. 

The  seventh  or  facial  nerve  arises  from  a  nucleus  a  little 
below  and  external  to  the  origin  of  the  sixth  nerve. 

The  eighth  or  auditory  nerve  arises  from  two  nuclei. 
One  is  located  at  the  lateral  angle  of  the  ventricle,  another 
near  the  fovea  inferior. 

The  ninth  or  glosso-pharyngeal  nerve  arises  from  the 
lower  part  of  the  floor  of  the  ventricle,  below  the  fovea 
inferior  and  the  auditory  nucleus  in  that  region. 

The  tenth  ov  pneumogastric  nerve  has  its  deep  origin  im- 
mediately beneath  that  of  the  ninth  nerve. 

The  eleventh  or  accessory  part  of  the  spinal  accessory 
nerve  arises  from  a  nucleus  at  the  upper  part  of  the  cala- 
mus scriptorius. 

The  tivelfth  or  hypoglossal  nerve  arises  from  a  collection 
of  cells  in  the  nucleus  teres  which  produces  the  elevated 
fasciculus  teres  in  the  floor  of  the  ventricle. 

The  fifth  or  trifacial  nerve  has  two  roots — a  motor  and  a 
sensory.  The  deep  origin  of  the  sensory  root  is  in  the 
highest  part  of  the  floor  of  the  ventricle — viz.,  near  the 
border  of  the  superior  peduncle  of  the  cerebellum  which 
forms  the  superior  or  antero-lateral  boundary  of  the  ven- 
tricle. The  deep  origin  of  the  motor  root  is  from  a  nucleus 
a  little  external  to  the  upper  part  of  the  fasciculus  teres. 

The  Za^eraZ  boundaries  of  the  fourth  ventricle  are:  above, 
the  superior  peduncles  of  the  cerebellum,  which,  as  they 
pass  out  from  under  the  posterior  border  of  the  testes 
of  the  corpora  quadrigemina,  diverge  and  pass  outward 
to  the  cerebellar  hemispheres;  heloiu,  the  fasciculi  graciles 
and  the  restiform  bodies,  which,  as  they  ascend,  diverge 
and  pass  to  the  cerebellar  hemispheres,  forming  their 
inferior  peduncles. 

The  roof  is  formed  a6oue  by  the  valve  of  Vieussens — a  thin 
lamella  of  white  matter  which  stretches  between  the  upper 
borders  of  the  superior  peduncles  of  the  cerebellum:  below, 


FATIGUE    AND    REST    OF    THE   BRAIX.  399 

by  a  process  of  pia  mater  which  passes  from  the  inferior 
verm.iform  appendix,  or  middle  lobe  of  the  cerebellum,  to 
the  lower  part  of  the  medulla.  This  process  of  the  pia 
mater  is  pierced  by  an  opening  called  the  foramen  of  2Ia- 
gendie,  by  which  the  cavity  of  the  fourth  ventricle  com- 
municates with  the  subarachnoidian  space.  The  cavity  of 
the  fourth  ventricle  is  hned  by  a  dehcate  membrane  Avhich 
is  covered  with  a  layer  of  nucleated  endothelial  cells;  this 
membrane  is  continuous  with  that  which  lines  the  third 
ventricle. 

Projecting  from  the  pia  mater  into  the  cavity  are  two 
vascular  choroid  plexuses.  At  the  apex  of  the  calamus 
scriptorius  the  cavity  of  the  fourth  ventricle  communicates 
with  the  central  canal  in  the  gray  matter  of  the  medulla 
and  of  the  spinal  cord.  Above,  it  communicates  with  the 
third  ventricle  through  the  aqueduct  of  Sylvius,  the  narrow 
fissure  between  the  crura  cerebri  laterally  and  in  front,  and 
the  anterior  surface  of  the  corpora  quadrigemina  behind. 
This  fissure  is  covered  with  the  gray  matter  which  is  con- 
tinuous with  that  hning  the  floor  of  the  fourth  ventricle. 
The  lining  of  this  fissure  is  continuous  with  that  lining  the 
third  ventricle  above  and  with  that  lining  the  fourth 
ventricle  below. 

FATIGUE   AXD   REST   OF   THE   BRAIX. 

The  brain,  hke  all  other  organs  of  the  body,  requires,  after 
a  period  of  continuous  activity,  periods  of  rest;  these  are 
manifested  by  the  condition  known  as  sleep. 

This  condition  is  characterized  by  a  cessation  of  all  psy- 
chical activities  while  the  automatic  and  reflex  activities 
continue.  There  is  no  organ  which  is  so  continuously  active 
as  the  brain,  and  the  accumulation  of  the  products  of  retro- 
grade metamorphosis  resulting  from  such  continuous  ac- 
tivity produces  fatigue. 

In  man  this  condition  occurs  ordinarily  once  in  twenty- 


400     LECTURES   ON   HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

four  hours,  preferably  during  the  night,  because  then  ex- 
ternal influences,  such  as  light,  etc.,  are  lessened. 

During  sleep  there  is  a  decrease  of  all  physiological 
activities  in  the  body,  such  as  the  activity  of  the  heart, 
secretory  organs,  respiratory  organs,  etc. 

Dreaming  is  a  psychical  activity  of  certain  parts  of  the 
cerebral  cortex  without  an  av^akening  of  the  active  cere- 
bral cortex. 

Hypnotism  and  somnambulism  are  conditions  resembling 
sleep;  during  these  the  individual  performs  locomotorial 
motions  unconsciously.  This  is  probably  due  to  a  temporary 
paralysis  of  the  gray  cortical  substance  of  the  cerebrum. 

Certain  drugs — such  as  chloral,  morphine,  etc. — produce 
a  condition  resembling  sleep. 

Narcotic  drugs — such  as  ether,  chloroform,  nitrous  oxide, 
etc. — produce  unconsciousness,  resulting  from  a  temporary 
paralysis  of  the  cerebral  cortex. 

Interference  v^ith  the  nutrition  of  the  brain  soon  causes  a 
cessation  of  all  its  functions. 

Ligation  of  the  carotid  and  vertebral  arteries  produces 
total  unconsciousness  in  from  one  to  two  minutes.  The  first 
results  of  the  operation  are  tetanic  convulsions  and  dyspnoea 
as  the  result  of  the  irritation  of  the  medulla  by  the  accumula- 
tion of  CO., ;  finally  a  condition  of  coma — viz.,  entire  un- 
sciousness — sets  in. 

These  experiments  and  observations  tend  to  show  that 
the  metabolic  processes  in  the  brain  are  very  active. 


LEOTUEE  XLII. 

THE   CRANIAL  NERVES. 

The  cranial  nerves  are  those  which  arise  from  centres 
in  the  substance  of  the  brain  ;  they  emerge  from  various- 
points  on  the  surface  of  the  brain,  pass  through  openings 
in  the  dura  mater,  and  finally  leave  the  cranial  cavity 
through  the  various  foramina  at  its  base.  There  are 
twelve  pairs  of  cranial  nerves,  which,  in  the  order  in  which 
they  emerge  from  the  brain  and  the  cranial  cavity,  are 
called  as  follows  : 

First  or  olfactory  nerve. 

Second  or  optic  nerve. 

Third  or  motor  oculi  nerve. 

Fourth  or  patheticus  nerve. 

Fifth  or  trifacial  or  trigeminus  nerve. 

Sixth  or  abducent  nerve. 

Seventh  or  facial  nerve. 

Eighth  or  auditory  nerve. 

Ninth  or  glosso-pharyngeal  nerve. 

Tenth  or  vagus  or  pueumogastric  nerve. 

Eleventh  or  spinal  accessory  nerve. 

Twelfth  or  hypoglossal  nerve. 
The  cranial  nerves  may  be  divided,  in  accordance  with 
their  functions,  into  nerves  of  special  sense,  motor  and 
mixed  nerves. 

The  cranial  nerves  which  are  nerves  of  special  sense  are  : 
The  olfactory,  or  first ;  the  optic,  or  second  ;  the  auditory, 
or  eighth. 
The  motor  nerves  are  :     The  motor  oculi,  or  third  ;  the 

26 


402     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

patheticiis,  or  fourth;  the  abducent,  or  sixth;  the  facial, 
or  seventh;  the  hypoglossal,  or  twelfth. 

The  mixed  nerves  are:  The  trifacial,  or  fifth;  the  glosso- 
pharyngeal, or  ninth ;  the  pneuniogastric,  or  tenth  ;  the 
spinal  accessory,  or  eleventh. 

The  point  from  which  the  cranial  nerves  arise  at  the 
surface  of  the  brain  is  called  their  superficial  origin;  the 
point  or  nucleus  from  which  the  cranial  nerves  arise  from 
the  substance  of  the  brain  is  called  their  deep  or  real 
origin. 

The  First  or  Olfactory  Nerve. 

The  olfactory  nerves  are  the  nerves  of  the  special  sense 
of  smell.  Their  superficial  origin  is  in  the  olfactory  bulbs 
on  the  under  surface  of  the  frontal  lobes  on  each  side  to 
the  anterior  median  fissure.  The  olfactory  bulbs  are  the 
anterior  termination  of  the  olfactory  tracts  ;  they  arise 
by  three  roots  from  the  anterior  perforated  space  on  each 
side,  and  pass  forward  on  the  under  surface  of  the  frontal 
lobes.  The  olfactory  bulbs  rest  upon  the  superior  surface 
of  the  cribriform  plate  of  the  ethmoid  bone  ;  from  each 
bulb  from  fifteen  to  twenty  non-meduUated  nerve-fibres 
arise,  which  pass  downward  through  the  openings  in  the 
cribriform  plate  to  be  distributed  to  the  mucous  membrane 
of  the  upper  part  of  the  nasal  cavity. 

In  the  cerebral  hemispheres  the  fibres  of  the  roots  of  the 
olfactory  tracts  can  be  traced  to  the  psychosensorial 
region  of  the  cortical  gray  substance.  The  seat  of  the  cen- 
tres for  the  sense  of  smell  is,  according  to  Miink,  located 
in  the  cortical  substance  of  the  gyrus  hippocampus  and 
the  uncinate  convolutions;  destruction  of  these  regions  on 
both  sides  is  followed  by  a  total  loss  of  the  sense  of  smell. 
The  fibres  ascend  in  the  cerebral  hemispheres  through  the 
internal  capsule.  Transverse  fibres  contained  in  the  ante- 
rior commissure  of  the  third  ventricle  unite  the  fibres  of 
the  olfactorv  nerves  on  both  sides. 


THE    CRANIAL   NERVES.  403 

The  olfactoi'y  bulbs  must  be  considered  as  the  subcorti- 
cal centres  of  the  olfactory  nerves.  Section  of  the  olfac- 
tory nerves  produces  loss  of  the  sense  of  smell.  Electrical 
stimulation  of  the  olfactory  filaments  which  are  supjolied 
to  the  upper  part  of  the  nose  produces  the  sensation  of  smell. 

The  physiological  irritation  of  the  olfactory  nerves  is 
produced  by  the  particles  of  odorous  gases  as  they  reach 
the  upper  part  of  the  nose. 

Anosmia,  or  loss  of  the  sense  of  smell,  is  caused  by  in- 
juries to  the  olfactory  bulbs  and  tract  or  to  the  psycho- 
sensorial  cerebral  regions. 

Hyposmia — a  decrease  of  the  sense  of  smell — is  caused  by 
over-irritation  of  the  olfactory  nerves,  and  also  by  certain 
drugs,  such  as  morphine;  the  effect  of  such  drugs  is  due  to 
their  influence  on  the  cortical  centre. 

Hyperosmia— the  excessive  acuteness  of  the  sense  of  smell 
— is  often  observed  in  hysterical  subjects,  but  is  often 
caused  by  certain  drugs — viz.,  strychnine — as  the  result  of 
an  irritation  of  the  cortical  centre. 

The  Second  or  Optic  Nerve. 

The  optic  nerves  are  the  nerves  of  the  special  sense  of 
sight.  The  nerve  arises  from  the  optic  commissure,  which 
is  situated  in  front  of  the  interpeduncular  space  at  the  base 
of  the  brain,  and  which  is  formed  by  the  connection  of  the 
optic  tracts.  These  arise  by  two  roots  from  the  outer  border 
of  the  crura  cerebri,  which  they  cross,  passing  obliquely  in- 
ward and  forward  until  they  meet  in  front,  forming  the 
optic  commissure. 

The  deep  origin  of  the  fibres  of  the  optic  tract  is  from 
the  nates  of  the  corpora  quadrigemina,  from  the  corpora 
geniculata,  and  from  the  posterior  tubercle  or  pulvinar 
of  the  optic  thalami.  These  ganglionic  masses  must  be  con- 
sidered the  subcortical  centres  for  the  sense  of  sight;  from 
them  fibres  pass  toward  the  cortical  substance  of  the  occi- 
pital lobes,  in  which  are  contained  the  psycho-optical  centres. 


404     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

In  the  optic  commissure  the  nerve-fibres  decussate.  The 
optic  nerves,  as  they  arise  from  the  commissure,  pass 
obhquely  forward  and  outward,  enter  the  orbit  through  the 
optic  foramen);  the  nerve  then  passes  through  the  sclerotic 
and  choroid  coats  of  the  eyeball  at  its  posterior  aspect,  and 
expands  into  the  retina. 

[  The  TJiird  or  Motor  Oculi  Nerve. 

The  motor  oculi  is,  as  the  name  implies,  a  motor  nerve. 
It  supplies  all  the  muscles  of  the  orbit  except  the  superior 
oblique  and  the  external  rectus  muscles;  it  also  supplies 
the  iris  and  the  ciliary  muscle. 

The  superficial  origin  of  the  motor  oculi  is  from  the  in- 
ternal border  of  the  crus  cerebri  near  the  anterior  border 
of  the  pons  Varolii.  Its  deep  origin  is  in  a  nucleus  in  the 
lower  part  of  the  floor  of  the  aqueduct  of  Sylvius  on  either 
side  of  the  middle  line;  from  this  subcortical  centre  fibres 
pass  to  the  cortex  of  the  angular  convolution  of  the  cere- 
brum. 

The  functions  of  the  motor  oculi  are  those  of  a  motor 
nerve.  Paralysis  is  followed  by  :  (1)  Slight  ptosis,  or  drop- 
ping of  |the  upper  eyelid,  because  fibres  of  the  nerve  also 
supply  the  elevator  palpebrarum  muscle. 

2.  Immobility  of  the  eyeball. 

3.  Strabismus :  the  eyeball  is  drawn  outward  and  down- 
ward. 

4.  Protrusion  of  the  eyeball,  on 'account  of  the  action  of 
the  superior  oblique,  which  is  not  paralyzed  and  which  is 
not  antagonized. 

5.  Mydriasis — viz.,  a  slight  dilatation  of  the  pupil. 

6.  The  pupil  no  longer  reacts  to  light  stimuli. 

Y.  Inability  to  accommodate  the  eye  for  vision  at  short 
distances. 

In  teething  children  there  is  often  observed  a  condition 
which  is  known  as  strabismus  spasticus,  due  to  a  reflex 
irritation  of  the  motor  oculi  nerves. 


THE   CRANIAL   NERVES.  405 

The  Fourth  or  Pathetic  or  Trochlear  Nerve, 

The  apparent  origin  of  the  fourth  cranial  nerve  is  from 
the  outer  border  of  the  crus  cerebri  on  each  side,  in  front 
of  the  anterior  border  of  the  pons  Varolii. 

The  deep  origin  is  in  a  nucleus  near  that  of  the  motor 
oculi  in  the  gray  matter  of  the  aqueduct  of  Sylvius;  from 
it  fibres  pass  to  the  psycho-motorial  cortical  centre  in  the 
angular  convolution  of  the  cerebral  surface.  The  fibres  of 
both  nerves  decussate  at  their  nuclei. 

The  fimotion  of  the  patheticus  is  that  of  a  motor  nerve; 
it  supplies  the  superior  oblique  muscle  of  the  eyeball. 

Paralysis  produces  a  decrease  in  the  mobility  of  the  eye- 
ball outward  and  downward,  and  slight  strabismus,  the 
eyeball  being  turned  slightly  inward  and  upward,  causing 
double  vision. 

The  Fifth  or  Trigeminus  Nerve. 

The  trigeminus  arises,  like  a  spinal  nerve,  by  two  roots — 
viz.,  a  small  anterior  or  motor  root,  and  a  larger,  the  poste- 
rior or  sensory  root.  The  trigeminus  resembles,  further- 
more, a  spinal  nerve,  in  having  a  ganglion  developed  on  its 
sensory  root. 

The  superficial  origin  is  from  between  the  transverse 
fibres  of  the  under  surface  of  the  pons  Varolii,  near  the 
anterior  border.  On  each  side  the  two  roots,  as  they  emerge 
from  this  point,  are  separated  by  a  few^  of  the  transverse 
fibres  of  the  pons. 

The  deep  origin  of  the  sensory  root  is  in  a  nucleus  located 
in  the  upper  part  of  the  floor  of  the  fourth  ventricle,  near 
its  margin,  and  on  a  level  with  the  superior  peduncles  of 
the  cerebellum. 

The  deep  origin  of  the  motor  root  is  in  a  nucleus  which 
is  located  in  the  floor  of  the  fourth  ventricle,  posterior 
and  internal  to  the  nucleus  of  the  sensory  root. 

From  these  nuclei  fibres  pass  to  the  cortical   centres 


406     LECTURES   ON    HUMAN    PHYSIOLOGY   AND   HISTOLOGY. 

located  in  the  psycho-sensorial  and  psycho-motorial  areas 
of  the  cerebral  cortex.  From  their  superficial  origin  the 
two  roots  pass  together  through  an  opening  in  the  dura 
mater,  and  then  forward  to  the  petrous  portion  of  the  tem- 
poral bone,  where  the  fibres  of  the  sensory  root  form  a 
ganglion  called  the  Gasserian  ganglion.  The  motor  root 
passes  forward  beneath  this  ganglion,  and  is  not  connected 
with  the  seusory  root  or  its  ganglion  within  the  cranial 
cavity. 

The  Gasserian  or  semilunar  ganglion  is  situated  upon 
the  upper  surface  of  the  petrous  portion  of  the  temporal 
bone,  near  the  apex,  and  above  the  internal  meatus  audito- 
rius.  The  ganglion  receives  nerve-fibres  from  the  carotid 
plexus  of  the  sympathetic  nerve. 

In  the  cranial  cavity  it  gives  off  fibres  to  the  tentorium 
cerebelli  and  to  the  dura  mater  lining  tiie  middle  fossa  of 
the  cranial  cavity.  From  the  anterior  border  of  the  gan- 
glion arise  three  large -branches — viz.,  the  ophthalmic,  the 
superior  maxillary,  and  the  inferior  maxillary  divisions. 

The  ophthalmic  and  the  superior  maxillar}^  divisions  "con- 
sist throughout  their  course  only  of  fibres  from  the  sensory 
root,  and  are,  therefore,  only  nerves  of  common  sensation. 
The  inferior  maxillary  division  is  joined  outside  of  the 
cranial  cavity  by  the  fibres  of  the  motor  root,  and  is,  from 
there  on,  a  nerve  of  motion  and  of  common  sensation. 

Tlie  Ophthalmic  Division.— Thi^  is  the  smallest  of  the 
three  divisions;  it  contains  fibres  from  the  cavernous  plexus 
of  the  sympathetic.  The  ophthalmic  division  passes  for- 
ward and  divides  into  three  branches — the  lachrymal, 
frontal,  and  nasal — just  before  it  enters  the  orbit  through 
the  sphenoidal  fissure. 

In  the  cranial  cavity  this  division  gives  off  a  recurrent 
branch,  which  supplies  the  tentorium  cerebelli;  it  contains 
sensory  fibres  and  vasomotor  fibres  from  the  sympathetic. 

The  lachrymal  branch  contains  fibres  of  common  sen- 
sation which  supply  the  eyeball,   conjunctiva,  lachrymal 


THE    CRANIAL    NERVES.  407 

gland,  and  the  integumeDt  of  the  upper  eyeUd,  and  tme 
secretory  fibres  for  the  lachrymal  gland. 

The  frontal  branch  divides  into  two  smaller  branches — 
the  supraorbital,  which,  passing  through  the  supraorbital 
foramen,  supplies  the  integument  of  the  forehead  with 
common  sensation ;  the  sujyratrochlear  branch  supphes- 
the  lower  and  inner  part  of  the  forehead  with  common 
sensation. 

The  nasal  nerve  supphes  the  greater  part  of  the  lining  of 
the  nasal  fossa  with  common  sensation. 

Connected  with  the  ophthalmic  division  of  the  fifth  nerve 
is  a  ganglion  called  the  ophthalmic,  lenticular,  or  ciliary 
ganglion:  this  is  about  the  size  of  a  pin-head;  it  is  located  at 
the  back  of  the  orbit.  The  roots — viz.,  the  branches  which 
pass  to  the  ganglion — are:  (1;  a  sensory  branch  from  the 
ophthalmic  division  of  the  fifth  nerve;  (2)  a  motor  branch. 
from  a  branch  of  the  thh-d  nerve  ;  and  (3)  a  symjxdhetic 
root  from  the  carotid  plexus. 

From  this  ganglion  are  given  off  from  6  to  10  branches — 
the  short  ciliary  nerves :  these  contain:  {a)  Motor  fibres  for 
the  sphincter  pupillge  and  the  tensor  choroidese  muscles,  also 
those  for  the  dilator  pupillae  muscles,  (b)  Sensory  fibres  for 
the  conjunction  of  the  bulb,  for  the  iris,  the  choroidea,  and 
for  the  sclerotic  coat  of  the  eye.  Irritation  of  these  fibres 
produces,  by  reflex  action,  secretion  of  the  lachrymal 
glands  and  closure  of  the  eyehd.  (c)  Vasomotor  fibres  for 
the  vessels  of  the  iris,  the  choroidea,  and  the  retina. 

The  vasomotor  fibres  of  the  ganglion  are  derived  from 
its  sympathetic  root ;  motor  fibres  from  its  motor,  and 
partly  from  its  sympathetic  roots;  the  sensory  fibres  all 
from  its  sensory  root. 

TJi.e  Snperior  Maxillary  Division. — This  division  is,  like 
the  former,  a  sensory  nerve.  From  the  Gasserian  ganghon 
it  passes  forward  and  leaves  the  cranial  cavity  through  the 
foramen  rotundum  in  the  superior  surface  of  the  great 
wing  of  the  sphenoid  bone.      It  then  crosses  the  spheno- 


9 
408     LECTURES   ON   HUMAN   PHYSIOLOGY    AND   HISTOLOGY. 

maxillary  fossa,  enters  the  infraorbital  canal  in  the  floor 
of  the  orbit,  and  finally  emerges  on  the  face  through  the 
infraorbital  foramen.  In  its  course  this  division  gives  off 
branches  in  the  cranial  cavity,  in  the  sph en o- maxillary 
fossa,  in  the  infraorbital  canal,  and  on  the  face. 

In  the  cranial  cavity  it  gives  off  a  sensory  branch — the 
meningeal  nerve — to  the  dura  mater.  In  the  spheno-max- 
illary  fossa  are  given  off  sensory  branches  to  the  integu- 
ment of  the  temple  and  side  of  the  forehead,  posterior  den- 
tal branches  to  the  molar  teeth  of  the  upper  jaw,  and  a 
branch  which  passes  to  the  spheno-palatine  ganglion  which 
is  connected  with  the  second  division  of  the  fifth  nerve. 

In  the  infraorbital  canal  this  division  gives  off  sensory 
branches  to  the  canine  and  front  teeth  of  the  upper  jaw. 

On  the  face  sensory  branches  are  distributed  to  the  con- 
junctiva and  integument  of  the  lower  eyelid,  to  the  integu- 
ment of  the  side  of  the  nose,  the  lips,  and  the  mucous 
membrane  of  the  mouth,  and  to  the  labial  glands. 

The  ganglion  which  is  connected  with  the  superior 
maxillary  division  of  the  fifth  cranial  nerve  is  called  the 
spheno-palatine  or  Meckel's  ganglion ;  this  is  located  in 
the  spheno-maxillary  fossa.  Its  sensory  root  is  formed  by 
the  spheno-palatine  branches  of  the  superior  maxillary 
division;  its  motor  root  is  from  the  large,  superficial  petro- 
sal branch  of  the  facial  nerve;  its  sympathetic  root  is 
formed  by  the  large,  deep  petrosal  branch  of  the  carotid 
plexus  of  the  sympathetic. 

From  Meckel's  ganglion  are  given  off  sensory,  motor, 
secretory,  and  vasomotor  fibres. 

The  sensory  fibres  are  distributed  to  the  mucous  mem- 
brane of  the  roof  of  the  mouth,  the  tonsils,  and  of  the 
iiose;  some  fibres  also  supply  the  periosteum  of  the  orbit. 

The  motor  fibres  are  distributed  to  the  levator  palati  and 
the  azygos  uvulae  muscles. 

The  vasomotor  fibres  are  distributed  to  the  vessels  in  the 
regions  supplied  by  the  sensory  branches. 


THE   CRANIAL  NERVES.  409 

The  secretory  fibres  are  distributed  to  the  glands  of  the 
mucous  membrane  of  the  nose. 

TJie  TJiird  or  Inferior  Maxillary  Division. — This  division 
is  given  off  from  the  lower  part  of  the  anterior  border  of 
the  Gasserian  ganglion;  it  passes  forward  and  leaves  the 
<jranial  cavity  through  the  foramen  ovale  in  the  superior 
surface  of  the  great  wing  of  the  sphenoid  bone.  Just  after 
passing  through  the  foramen  this  division  of  the  sensory 
root  of  the  fifth  nerve  unites  with  the  motor  root  and 
divides  into  an  anterior  and  a  posterior  portion.  Prior  to 
this  division  two  branches  are  given  off— viz.,  a  recurrent 
branch,  which  is  a  sensory  nerve  distributed  to  the  dura 
mater,  and  the  internal  pterygoid,  which  is  a  motor  nerve 
for  the  internal  pterygoid  muscle. 

The  anterior  portion  of  the  inferior  maxillary  nerve  con- 
tains most  of  its  motor  fibres;  these  are  distributed  to  the 
masseter,  buccinator,  temporal,  and  external  pterygoid 
muscles. 

The  posterior  portion  is  principally  a  sensory  nerve,  but 
■contains  a  few  fibres  from  the  motor  root.  This  portion 
divides  into  three  branches — viz.,  the  auriculo-temporal, 
the  lingual,  and  the  inferior  dental. 

The  auricido-temporal  is  a  sensory  nerve  ;  its  branches 
are  distributed  to  the  anterior  portion  of  the  external  ear, 
the  meatus  auditorius  externus,  the  integument  of  the  tem- 
poral region,  and  to  the  temporo-maxillary  articulation. 

The  lingual  nerve  does  not  contain  motor  fibres  ;  it  is  a 
-sensory  nerve,  and  by  its  union  with  the  fibres  of  the 
chorda  tympani — a  branch  from  the  facial  nerve — it  also 
becomes  a  nerve  for  the  special  sense  of  taste  ;  it  is  also  the 
nerve  for  the  sense  of  touch  for  the  tongue,  the  roof  and 
floor  of  the  buccal  cavity. 

The  inferior  dental  nerve  is  a  sensory  nerve  distributed 
to  the  teeth  of  the  lower  jaw,  the  gums  of  the  lower  jaw, 
^nd  the  integument  of  the  chin  and  the  lower  lip.  Before 
•entering  the  inferior  dental  canal  the  nerve  gives  off  two 


410     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

motor  branches  to  the  niylo-hyoid  and  to  the  anterior  belly 
of  the  digastric  muscle. 

Connected  with  the  inferior  maxillary  division  are  two 
ganglia — viz. ,  the  otic  and  the  submaxillary. 

The  otic  or  Arnold's  ganglion  is  located  immediately  be- 
neath the  foramen  ovale  ;  it  communicates  with  the  inter- 
nal pterygoid  branch  of  the  inferior  maxillary  division, 
with  the  facial  and  glosso-pharyngeal  nerves  through  the 
small  superficial  petrosal  nerve,  and  with  sympathetic 
fibres  from  the  carotid  plexus.  Its  motor  fibres  are  from 
the  seventh  and  the  inferior  maxillary  division  of  the 
fifth  ;  its  sensory  fibres  also  from  the  third  division  of  the 
fifth  and  from  the  glosso-pharyngeal  nerve. 

From  the  ganglion  branches  communicate  with  the  auri- 
culo-temporal  nerve,  and  motor  branches  are  given  off  to- 
the  tensor  palati  and  the  tensor  tympani  muscles. 

The  submaxillary  ganglion  is  situated  above  the  lower 
portion  of  the  subuiaxillary  gland.  The  ganglion  receives 
fibres  from  the  chorda  tympani  ;  these  are  secretory  fibres, 
vasodilator  fibres  which  are  distributed  to  the  gland,  and 
motor  fibres  which  are  distributed  to  the  non-striated  fibres 
of  the  duct  of  the  submaxillary  gland. 

The  ganglion  receives  sensory  fibres  from  the  lingual 
nerve,  and  sympathetic  fibres  from  the  plexus  surrounding 
the  facial  artery. 

The  sensory  fibres  from  the  ganglion  are  distributed  to- 
the  gland,  its  duct,  and  to  the  side  of  the  tongue. 


LEOTUEE    XLTI. 
THE  CRANIAL  NERVES  {continued). 

The  Sixth  or  Nervus  Ahducens. 

The  abducent  is  a  motor  nerve  for  the  external  rectus 
muscle  of  the  eye. 

The  superficial  origin  of  the  sixth  nerve  is  from  the  sides 
of  the  pyramid  near  the  border  of  the  pons. 

The  deep  origin  is  in  the  floor  of  the  fourth  ventricle 
posterior  to  that  of  the  mo1;or  root  of  the  trifacial  nerve. 

The  nerve  enters  the  orbit  through  the  sphenoidal  fissure. 
Paralysis  of  the  nerve  produces  strabismus,  the  bulb  of  the 
eye  being  turned  inward. 

Hie  Seventh  or  Facial  Nerve. 

The  seventh  or  facial  nerve  is  the  motor  nerve  for  all 
muscles  of  the  face,  also  for  the  buccinator,  the  platysma 
myoides,  the  stylo-hyoid,  and  the  posterior  belly  of  the 
digastric. 

The  deep  origin  is  in  a  nucleus  on  the  floor  of  the  fourth 
ventricle,  below  and  external  to  that  of  the  abducent  nerve. 
The  superficial  origin  is  from  the  lateral  tract  of  the 
medulla  oblongata. 

From  its  superficial  origin  the  nerve  passes  forward  and 
enters  the  internal  meatus  auditorius  in  the  petrous  por- 
tion of  the  temporal  bone,  together  with  the  auditory 
nerve.  In  the  fioor  of  the  meatus  the  facial  nerve  then 
enters  the  aqueductus  Fallopii,  and  finally  leaves  the 
cranial  cavity  through  the  stylo-mastoid  foramen,  pene- 
trates  the    parotid    gland,    and    divides    into    its    many 


412     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

branches.  The  facial  nerve  gives  off  within  the  aqueduc- 
tus  Fallopii  two  branches — the  tympanic  and  the  chorda 
tympani. 

The  tympanic  branch  suppUes  the  stapedius  muscle. 

The  chorda  tympani  is  a  nerve  for  the  special  sense  of 
taste,  and  also  the  nerve  for  the  tactile  sense  of  the  tongue. 

In  its  course  the  nerve  unites  with  the  lingual  branch  of 
the  third  division  of  the  trigeminus.  It  has  been  observed 
that  some  fibres  of  the  facial  nerve  have  their  deep  origin 
in  the  nucleus  of  the  glosso-pharyngeal,  and  it  is  supposed 
that  these  fibres  constitute  those  of  the  chorda  tympani. 

In  the  internal  meatus  the  facial  nerve  communicates 
by  several  fibres  with  the  auditory  nerve.  The  large  su- 
perficial petrosal  nerve  is  also  given  off  from  the  facial 
in  this  region;  by  it  the  facial  communicates  with  Meckel's 
ganglion. 

In  the  aqueduct  of  Fallopius  the  facial  nerve  commu- 
nicates with  the  otic  ganglion  by  the  small  superficial 
petrosal  nerve,  and  with  the  sympathetic  plexus  in  that 
region.  After  its  exit  from  the  stylo-mastoid  foramen 
the  facial  nerve  supplies  motor  nerves  to  the  stylo-hyoid, 
the  posterior  belly  of  the  digastric,  the  occipital,  the  buc- 
cinator, the  platysma  myoides,  the  muscles  of  the  external 
ear,  and  to  all  the  muscles  of  the  face. 

In  the  face  the  branches  of  the  facial  nerve  anastomose 
with  branches  of  the  trigeminus.  After  the  exit  through 
the  stylo-mastoid  foramen  the  facial  nerve  also  commu- 
nicates with  the  glosso-pharyngeal,  with  the  vagus,  with 
the  sympathetic  plexus  surrounding  the  carotid  artery, 
and  with  the  three  divisions  of  the  trigeminus. 

The  facial  nerve  is  the  nerv^e  for  the  voluntary  motions 
of  the  muscles  of  the  face,  by  which  we  are  able  to  give  to 
it  the  various  expressions.  To  a  certain  extent  the  facial 
nerve  also  partakes  in  the  nervous  mechanism  of  speech 
and  of  the  act  of  deglutition. 


THE   CRANIAL   NERVES.  413 

TJie  Eighth  or  Auditory  Nerve. 

The  superficial  origin  of  the  eighth  or  auditory  nerve  is 
from  the  side  of  the  meduUa  oblongata,  from  a  groove  be- 
tween the  ohvary  body  and  the  restiform  body. 

The  deep  origin  of  this  nerve  is  in  two  nuclei,  one  of 
which  is  situated  at  the  lateral  angle  of  the  fourth  ven- 
tricle, the  other  on  the  floor  of  the  ventricle  posterior  and 
internal  to  the  former  nucleus. 

From  its  superficial  origin  the  nerve  passes  forward  and 
enters  the  meatus  auditorius  internus  together  with  the 
facial  nerve,  and  is  connected  with  it  by  several  fibres. 
In  the  meatus  the  nerve  divides  into  two  branches— viz., 
the  cochlear,  which  is  distributed  to  the  cochlea,  and  the 
vestibular,  which  is  distributed  to  the  vestibule  and  the 
semicircular  canals. 

The  auditory  nerve  has  two  functions.  First,  it  is  the 
nerve  for  the  special  sense  of  hearing.  Irritation  of  the 
nerve  produces  the  sensation  of  hearing:  injury  or  destruc- 
tion produces  deafness. 

Second,  the  auditory  nerve  controls  the  motions  which 
are  required  for  the  maintenance  of  the  body  equilibrium. 
This  function  of  the  nerve  is  localized  in  the  portion  which 
is  distributed  to  the  semicircular  canals.  Destruction  of 
these  does  not  produce  any  disturbances  of  the  sense  of 
hearing,  but  is  foUowed  by  vertigo,  dizziness,  and  dis- 
turbances of  the  body  equilibrium. 


The  Ninth  or  Glosso- Pharyngeal  Nerve. 

The  glosso-pharyngeal  is  a  mixed  nerve  ;  it  is  the  nerve 
of  common  sensation  for  the  surface  of  the  tongue, 
pharynx,  fauces,  and  the  tonsils,  and  a  nerve  of  the  special 
sense  of  taste  for  those  parts  of  the  tongue  which  it  sup- 
phes  ;  it  also  sends  motor  filaments  to  the  pharynx.  The 
deep  origin  of  this  nerve  is  in  a  nucleus  in  the  floor  of  the 


414     LECTURES   OX  HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

fourth  ventricle,  below  the  nucleus  of  the  auditory,  and 
above  that  of  the  vagus  nerve. 

The  superficial  origin  is  from  the  side  of  the  medulla  ob- 
longata, from  the  groove  between  the  olivary  body  and  the 
restiform  body  above  the  superficial  origin  of  the  vagus. 

The  glosso-pharyngeal  leaves  the  cranial  cavity  through 
the  jugular  foramen.  In  passing  through  this  foramen  the 
nerve  presents  two  ganglia — viz.,  the  jugular  and  the 
petrous. 

The  x>€,trous  ganglion  is  the  larger  of  the  two  ;  through 
it  the  glosso-pharyngeal  nerve  communicates  with  the 
pneumogastric,  with  the  sympathetic,  and  with  the  facial 
nerve. 

The  jugular  ganglion  is  a  small  ganglionic  mass  sepa- 
rated from  the  former. 

The  motor  branches  of  the  glosso-pharyneal  nerve  sup- 
ply the  constrictors  of  the  pharynx,  the  palato-glossus, 
the  palato-pharyngeus,  the  stylo-pharyngeus  muscles. 

The  Tenth  or  Vagus  or  Pneumogastric  Nerve. 

The  deep  origin  of  this  nerve  is  in  a  nucleus  in  the  lower 
part  of  the  floor  of  the  fourth  ventricle  ;  this  nucleus  is 
situated  below,  and  is  continuous  with,  the  nucleus  of  the 
glosso-pharyngeal  nerve. 

The  superficial  origin  is  from  the  side  of  the  medulla 
oblongata,  below  that  of  the  glosso-pharyngeus. 

The  vagus  passes  forward  from  its  origin  and  leaves  the 
cranial  cavity  in  a  sheath,  together  with  the  spinal  ac- 
cessory nerve,  through  the  jugular  foramen.  The  vagus 
has  a  greater  distribution  than  any  other  cranial  nerve. 
It  is  composed  of  sensory  and  the  motor  fibres  ;  it  passes 
through  the  neck,  the  thorax,  and  the  upper  part  of  the 
abdomen.  The  motor  fibres  are  distributed  to  the  vocal 
organs,  to  the  respiratory  apparatus,  to  the  pharynx,  the 
oesophagus,  to  the  heart,  and  to  the  stomach.     Its  sensory 


THE    CRAXIAL    XERVES.  415 

fibres  are  distributed  to  the  larynx  and  to  the  respiratory 
tract. 

Immediately  below  the  jugular  foramen  the  vagus  pre- 
sents a  ganglion  called  the  ganglion  of  the  root  of  the 
vagus  :  this  ganglion  is  connected  with  the  accessory  por- 
tion of  the  spinal  accessory  nerve,  with  the  petrous  gan- 
glion of  the  glosso-pharyngeal,  T\dfch  the  facial,  and  ^vith 
the  superior  cervical  plexus  of  the  sympathetic  nerve. 

Beneath  this  ganglion  there  is  a  second  ganghonic  en- 
largement, called  the  ganglion  of  the  trunk  of  the  vagus: 
this  communicates  with  the  hypoglossal  nerve,  with  the 
superior  cervical  plexus  of  the  sympathetic,  with  the  first 
and  second  cervical  nerves.  Beneath  this  ganglion  the 
vagus  gives  off  many  branches  with  various  functions, 
•as  follows : 

Motor  fibres  to  the  muscles  of  the  neck,  principally  de- 
rived through  the  spinal  accessory. 

Sensory  fibres  through  the  auricular  branch  to  the  tym- 
panum and  middle  ear. 

Motor  fibres  in  the  pharyngeal  branch  to  the  muscles  of 
the  pharynx,  soft  palate,  and  upper  part  of  the  oesopha- 
gus. The  vagus,  therefore,  to  a  great  extent,  partakes  of 
the  nervous  mechanism  of  the  act  of  deglutition. 

Sensory  and  motor  fibres,  through  the  superior  laryngeal 
nerve,  to  the  mucous  membrane  of  t^he  larynx  and  the 
muscles  which  produce  tension  of  the  vocal  cords. 

Motor  fibres  to  the  muscles  of  the  larynx  which  close 
and  enlarge  the  glottis,  and  which  relax  the  vocal  cords, 
through  the  inferior  laryngeal  nerve. 

Motor  fibres  to  the  non-striated  fibres  of  the  oesophagus. 

Motor  and  sensory  fibres  to  the  lungs.  The  influence  of 
these  nerves  on  the  respiratory  function  has  akeady  been 
described  under  the  subject  of  respiration. 

Inhibitory  fibres  to  the  heart. 

Sensory  fibres  to  the  heart. 

Motor  and  sensory  fibres  to  the  stomach. 


416     LECTURES   ON   HUM.IN    PHYSIOLOGY    AND    HISTOLOGY". 

Section  of  the  vagus  in  the  neck  is  followed  by  many 
serious  disturbances  which  finally  cause  death.  Among- 
the  most  prominent  disturbances  may  be  mentioned  the 
increased  cardiac  action  and  the  decreased  and  labored  res- 
pirations. Aside  from  these,  various  motor  disturbances 
are  caused,  due  to  paralyzation  of  muscles  of  the  neck,  of 
the  larynx,  pharynx,  and  oesophagus. 

The  Eleventh  or  Spinal  Accessory  Nerve. 

This  nerve  consists  of  two  parts — viz.,  the  accessory  part 
to  the  vagus,  and  the  spinal  portion. 

The  deep  origin  of  the  accessory  portion  is  in  a  nucleus 
in  the  floor  of  the  fourth  ventricle  at  the  top  of  the  cala- 
mus scriptorius;  it  extends  downward  as  far  as  the  inter- 
mediary lateral  tract  of  the  gray  matter  of  the  cord,  to  the 
deep  origin  of  the  spinal  portion  of  the  nerve. 

Tlie  superficial  origin  of  the  accessory  portion  is  from^ 
the  side  of  the  medulla  below  that  of  the  vagus. 

The  superficial  origin  of  the  spinal  portion  is  from  the 
lateral  tract  of  the  cord  as  far  as  the  sixth  cervical  nerve. 

The  accessory  portion  of  the  nerve  passes  from  its  origin 
forward  through  the  jugular  foramen  with  the  vagus;  it 
is  then  connected  by  filaments  with  the  ganglion  of  the 
root  of  the  vagus  and  with  the  spinal  portion  of  the  spinal 
accessory;  it  then  joins  the  trunk  of  the  vagus,  passes 
through  the  ganglion  of  the  trunk,  and  is  distributed  to 
the  superior  laryngeal  and  the  pharyngeal  branches  of  the 
vagus. 

This  portion  of  the  spinal  accessory  contains  motor  and 
cardio-inhibitory  fibres. 

The  spinal  portion  of  the  spinal  accessory  nerve  ascends 
from  its  superficial  origin,  then  enters  the  cranial  cavity 
through  the  foramen  magnum,  then  passes  outward  and 
leaves  the  cranial  cavity  through  the  jugular  foramen  in 
the  same  sheath  with  the  pneumogastric  nerve;  it  contains, 
sensory  fibres  from  the  first  and  second  cervical  nerves. 


THE   CRANIAL   NERVES.  417 

This  portion  of  the  spinal  accessory  supplies  principally 
motor  fibres  to  the  trapezius  and  sterno-mastoid  muscles. 

The  Twelfth  or  Hypoglossal  Nerve. 

This  nerve  supplies  motor  fibres  to  the  muscles  of  the 
tongue,  the  genio-hyoid,  and  thyreo-hyoid  muscles. 

Its  deep  origin  is  in  a  nucleus  in  the  floor  of  the  fourth 
ventricle,  in  the  lower  part  near  the  median  line. 

Its  superficial  origin  is  from  the  side  of  the  medulla,  from 
the  groove  between  the  pyramid  and  the  olivary  body. 

The  hypoglossal  leaves  the  cranial  cavity  through  the 
anterior  condyloid  foramina. 

It  is,  at  its  root,  a  purely  motor  nerve,  but  in  its  course 
it  receives  vasomotor  fibres  from  the  cervical  sympathetic, 
which  are  distributed  to  vessels  of  the  tongue.  Section  of 
the  hypoglossal  produces  total  paralysis  of  the  tongue. 

27 


LECTURE    XLIV. 

THE   SPINAL   CORD. 

Anatomy  and  Structure. 

The  spinal  cord  is  that  portion  of  the  cerehro-spinal 
axis  which  is  contained  in  the  spinal  canal ;  it  does  not 
fill  the  spinal  canal.  The  cord  is  covered  by  three  mem- 
branes— viz.,  the  dura  mater,  the  arachnoid,  and  the  pia 
mater.  The  dura  mater  of  the  cord  is  not  adherent  to  the 
walls  of  the  spinal  canal,  but  surrounds  the  cord  loosely  as 
a  tubular  sheath;  the  membranes  of  the  cord  are  continu- 
ous with  those  of  the  brain.  The  dura  mater  is  pierced  on 
its  sides  for  the  transmission  of  the  roots  of  the  spinal 
nerves. 

The  spinal  cord  is  from  17  to  18  inches  long;  it  extends 
from  the  upper  border  of  the  atlas  to  the  lower  border  of 
the  first  lumbar  vertebra,  where  it  terminates  in  a  thin, 
slender  extremity  called  the  filuiu  terminale.  The  weight 
of  the  spinal  cord  divested  of  its  membranes  is  about  li 
ounces.  The  cord  is  rounded  and  somewhat  flattened;  it 
is  not  of  an  equal  thickness,  but  is  slightly  thicker  in  its 
upper  part,  and  presents  in  the  cervical  and  in  the  lumbar 
regions  enlargements  which  are  due  to  greater  masses  of 
gray  matter  in  the  interior  of  the  cord. 

The  cord  is  divided  on  its  surface  into  symmetrical  late- 
ral halves  by  two  fissures.  One,  the  anterior  median 
fissure,  passes  along  the  whole  length  of  the  anterior 
aspect  of  the  cord;  and  the  other,  the  posterior  median 
fissure,  passes  along  the  whole  length  of  the  posterior 
aspect.     The  anterior  fissure  is  wider,  but  not  as  deep  as 


THE    SPINAL    COED.  419l 

the  posterior.  These  halves  are  connected  by  a  transverse- 
band  of  nerve-tissue  which  is  called  the  commissure  of  the 
cord.  The  anterior  half  of  this  consists  of  white  niedul- 
lated  fibres  and  is  called  the  anterior  or  luhite  commissure. 
The  posterior  half  is  composed  of  nerve-fibres  and  neuroglia^ 
it  has  a  grayish  color,  and  is  called  the  j^osterior  or  gray 
commissure.  Each  lateral  half  of  the  cord  presents  late- 
rally to  the  anterior  and  posterior  median  fissure  a  shallow 
longitudinal  fissure  called  the  anterior  and  posterior  late- 
ral fissures.  These  several  fissures  divide  each  lateral  half 
of  the  cord  on  its  surface  into  four  columns,  which  are 
called  respectively  the  anterior,  the  lateral,  and  the  pos- 
terior columns  of  the  cord. 

The  anterior  column  is  the  portion  between  the  anterior- 
median  and  the  antero-lateral  fissures. 

The  lateral  column  is  the  largest;  it  is  the  portion  be- 
tween the  antero  lateral  and  the  postero-lateral  fissures. 

HhQ  posterior  column  is  the  portion  between  the  poste- 
rior median  and  the  postero-lateral  fissures.  At  each  side 
of  the  posterior  median  fissure  a  narrow  segment  of  the 
posterior  columns  protrudes  somewhat;  this  is  also  called 
the  posterior  median  column,  or  the  column  of  G oil.  The- 
portion  of  the  posterior  column  external  to  this  column  of 
Goll  is  called  the  posterior  external  column,  or  the  cuneate 
fasciculus. 

From  the  grooves  in  each  lateral  half  of  the  cord — viz.^. 
from  the  anterior  and  the  posterior  lateral  fissures — arise 
the  roots  of  the  spinal  nerves.  The  anterior  or  motor 
roots  arise  from  the  anterior,  the  posterior  or  sensorjr 
roots  from  the  posterior,  lateral  fissure. 

The  spinal  cord,  like  all  central  organs  of  the  cerebro- 
spinal nervous  system,  consists  of  white  and  gray  nerve- 
substance,  the  former  being  arranged  externally,  the  latter 
internally. 

The  white  matter  of  the  cord  constitutes  the  mass  of  the 
columns;   it  is  composed   of    medullated   nerve-fibres,    of. 


420     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

neuroglia,  of  blood-vessels,  and  of  delicate  septa  from  the 
pia  mater  which  pass  inward  between  the  bundles  of 
fibres  supporting  it. 

The  medullated  fibres  of  the  w^hite  substance  of  the  cord 
are  largely  longitudinal  fibres  arranged  in  bundles  or  fas- 
ciculi. There  are  also  transverse  or  oblique  fibres ;  these 
are:  (a)  the  fibres  which  pass  transversely  from  one  lateral 
half  of  the  cord  to  the  other  across  the  anterior  or  white 
commissure;  (b)  the  fibres  from  the  roots  of  the  spinal 
nerves — these  pass  transversely,  at  some  points  in  an  ob- 
lique course,  through  the  white  substance  into  the  gray 
matter  ;  (c)  fibres  which  pass  transversely  through  the  an- 
terior commissure  from  the  anterior  horn  of  the  gray 
matter  on  one  side  to  the  anterior  horn  in  the  other  side  of 
the  cord;  and  (d)  fibres  which  arise  from  cells  in  the  gray 
matter  and  enter  the  white  substance,  passing  in  it  ob- 
liquely or  horizontally,  being  sometimes  continuous  with 
the  longitudinal  fibres. 

The  fibres  of  the  white  matter  are  separated  into  several 
distinct  bundles,  tracts,  or  fasciculi.  The  observation  of 
pathological  lesions  of  these  bundles  and  many  experi- 
ments have  demonstrated  that  the  fibres  of  these  bundles 
possess  certain  special  functions. 

The  several  bundles  or  fasciculi  of  nerve- fibres  of  which 
each  column  of  the  cord  is  composed  are  as  follows: 

The  anterior  column  of  the  cord  consists  of  two  bundles 
— viz.,  (1)  the  direct  pyramidal  fasciculus,  and  (2)  the  fun- 
damental fasciculus. 

1.  The  direct  pyramidal  fasciculus  comprises  the  portion 
of  the  anterior  column  near  the  anterior  median  fissure;  it 
consists  of  longitudinal  fibres  which  ascend  and  are  con- 
tinuous with  fibres  of  the  pyramid  of  the  medulla  oblongata 
on  the  same  side.  The  fibres  of  the  pyramids  are  continuous 
with  the  superficial  longitudinal  fibres  of  the  pons  Varolii; 
these  pass  forward  as  the  fibres  of  the  crusta  of  the  crura 
cerebri.     In  the  cerebral  hemispheres  part  of  these  fibres 


THE   SPINTAL   CORD.  421 

pass  directly  through  the  internal  capsule  to  the  cortical 
gray  substance  of  the  psycho-motorial  region,  and  the  re- 
mainder pass  to  the  corpus  striatum.  The  fibres  of  the 
pyramids  are  motor.  Those  fibres  of  the  pyramids  which 
are  continuous  with  the  fibres  of  the  direct  pyramidal  fas- 
ciculus of  the  same  side  decussate  as  they  pass  to  the 
cerebral  hemispheres  through  the  pons  and  the  crura 
cerebri. 

3.  The  fimdamental  fasciculus  comprises  the  remaining 
portion  of  the  anterior  column  ;  its  fibres  ascend  and  enter 
the  deeper  portion  of  the  medulla — viz.,  the  formatio  reti- 
cularis. The  fibres  of  the  formatio  reticularis  of  the 
medulla  are  continuous  with  the  fibres  of  the  same  struc- 
ture of  the  pons,  and  these  are  continuous  with  the  fibres 
of  the  tegmentum  or  upper  layer  of  the  crura  cerebri. 
Entering  the  cerebral  hemispheres,  the  fibres  of  the  teg- 
mentum pass  upward,  either  directly  to  the  psycho-senso- 
rial  area  of  the  cortex  or  to  the  subcortical  sensory  centres, 
the  optic  thalami. 

The  lateral  column  of  the  cord  consists  of  four  bundles-— 
viz.,  1,  the  anterior  radicular  zone  ;  2,  the  cerebellar  col- 
umn ;  3,  the  mixed  lateral  column  ;  and  4,  the  crossed 
pyramidal  fasciculus. 

1.  The  anterior  radicular  zone  comprises  the  anterior 
portion  of  the  lateral  column  ;  its  fibres  ascend  through  the 
lateral  tracts  of  the  medulla  on  the  same  side,  and  are  con- 
tinued upward  as  fibres  of  the  formatio  reticularis  of  the 
pons. 

2.  The  cerebellar  column  coftiprises  the  posterior  and 
peripheral  portion  of  the  lateral  column.  The  fibres  of 
this  fasciculus  ascend  under  the  lateral  tract  of  the  medulla 
on  the  same  side,  then  pass  into  the  restiform  body  of  the 
medulla,  and  from  here  pass  to  the  cerebellum  as  fibres  of 
the  inferior  peduncles  of  the  cerebellum. 

3.  The  mixed  lateral  column  comprises  the  portion  of  the 
lateral  column  behind  the  anterior  radicular  zone  and  in- 


-i-22     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

ternal  to  the  cerebellar  column.  The  fibres  of  this  bundle 
ascend  into  the  lateral  tract  of  the  medulla  and  then  pass 
up  into  the  formatio  reticularis  of  the  medulla  and  the 
pons. 

4.  The  crossed  pyramidal  fasciculus  comprises  the  por- 
tion of  the  lateral  column  internal  to  the  mixed  lateral 
■column  ;  its  fibres  ascend,  cross  the  anterior  median  fissure 
in  the  lower  part  of  the  medulla,  and  enter  the  pyramid  on 
the  opposite  side. 

The  ptostetnor  column  of  the  cord  consists  of  two  bundles 
— viz  ,  (1)  the  posterior  median,  or  the  column  of  GoU,  and 
(2)  the  cuneate  fasciculus,  or  Burdach's  column. 

1.  The  column  of  Goll  comprises  the  portion  near  the 
posterior  median  fissure  ;  its  fibres  are  continued  upward 
as  fibres  of  the  fasciculus  gracilis  of  the  medulla  ;  the 
fibres  of  this  terminate  in  the  nucleus  gracilis. 

•2.  The  cuneate  fasciculus  comprises  the  outer  portion  of 
the  posterior  column  ;  its  fibres  are  continued  upward  as 
"the  fibres  of  the  funiculus  cuneatus  of  the  medulla,  and 
"terminate  in  a  mass  of  gray  matter  called  the  nucleus 
cuneatus. 

The  course  of  the  longitudinal  fibres  of  these  various 
bundles  cannot  be  traced  by  dissection.  The  method  gen- 
erally adopted  to  determine  their  course  is  careful  section 
of  the  various  bundles,  and  is  based  upon  the  fact  that 
nerve-fibres  undergo  degeneration  when  the  connection 
with  their  centre  is  severed. 

The  special  function  of  the  fibres  of  the  several  bundles 
is  determined  by  observing  the  disturbances  produced  by 
^experimental  section  or  by  pathological  lesions  of  the  vari- 
ous parts  of  the  cord. 

The  gray  matter  of  the  cord  is  contained  in  its  centre,  and 
is  so  arranged  that  each  lateral  half  contains  a  crescentic 
mass  of  gray  matter,  w^hich  is  directed  with  its  concavity 
outward  and  with  its  convexity  toward  the  median  line. 

The  two  crescentic  masses  are  connected  by  a  transverse 


THE    SPIXAL    COED.  42-3 

band  of  gray  matter,  which  forms  the  posterior  part  of  the 
commissure  of  the  cord,  and  is  also  cahed  the  posterior  or 
gray  commissm-e.  This  is  pierced  in  the  centre  by  a  delicate 
canal  which  extends  through  the  entire  length  of  the  cord; 
this  is  called  the  central  canal  of  the  cord;  it  is  Uned  with 
cndothehum  and  communicates  with  the  fourth  ventricle 
■of  the  brain.  On  a  transverse  section  of  the  cord  the  gray 
matter  in  the  centre  has  the  form  of  the  letter  X. 

The  crescentic  mass  of  gray  matter  in  each  lateral  half 
of  the  cord  presents  an  anterior  and  a  posterior  horn  or 
genu. 

The  anterior  horn  is  thick,  rounded,  and  directed  forward 
and  outward  toward  the  anterolateral  fissure,  not  reach- 
ing, however,  its  surface;  from  the  anterior  horn  arise  the 
fibres  of  the  anterior  or  motor  roots  of  the  spinal  nerves. 

The  posterior  horn  is  thin  and  slender,  and  is  directed 
outward  and  backward  toward  the  posterolateral  fissure 
extending  to  its  bottom  surface:  from  the  posterior  horn 
arise  the  fibres  of  the  posterior  or  sensory  roots  of  the 
spinal  nerves. 

The  gray  matter  of  the  cord  consists  of  ganghon-ceUs,  of 
a  dehcate  network  of  nerve-fibrillce  which  are  continuous 
with  the  protoplasmic  processes  of  the  ganglion-cells,  and  of 
medullated  nerve-fibres  which  frequently  branch  oif .  finally 
become  non-meduUated  and  communicate  with  the  dehcate 
fibrillar  network  ;  behind,  and  in  front  of  the  central 
canal,  nerve-fibres  pass  from  one  side  to  the  other  across 
the  gray  commissure.  The  ganghon-cells  are  situated  in 
groups  in  the  anterior  and  posterior  horn:  those  in  the 
anterior  horn  are  large,  pear-shaped,  unipolar  ceUs,  the  pole 
of  which  is  continuous  with  the  axis-cylinder  of  a  fibre  of 
the  anterior  or  motor  root  of  a  spinal  nerve.  These  gangha 
communicate  with  the  fibriUar  network  of  the  gray  sub- 
stance by  dehcate  protoplasmic  processes  from  their  body. 
These  gangha  must  therefore  be  regarded  as  motor  centres. 

The  gangha  in  the  posterior  horn  are  smaller:  the  body 


424     LECTURES    ON   HUMAN    PHYSIOLOGY    AND    HISTOLOGY. 

of  each  is  spindle-shaped  and  communicates  by  its  poles 
with  the  fibrillar  network  in  the  gray  substance.  These 
ganglia  are  surrounded  by  the  tree-shaped  terminals  of  the 
fibres  of  the  sensory  roots.  It  is  evident  that  these  fibres 
impart  impulses  to  the  ganglia,  which  they  embrace  with 
their  branching  terminations,  and  must  therefore  be  con- 
sidered as  sensory  centimes. 

From  the  axis-cylinder  of  many  of  the  longitudinal 
fibres  of  the  white  substance,  delicate  fibrillse  pass  hori- 
zontally into  the  gray  substance,  terminating  in  tree-like 
branches  which  embrace  the  ganglion -cells  in  the  gray 
matter.  These  tree-like  terminations  of  nerve-fibrillae  in 
the  gray  matter  are  called  collaterals. 

The  delicate  nerve-fibrillce  and  collaterals  in  the  gray 
matter  serve  to  conduct  impressions  in  this  portion  of  the 
cord  and  between  the  ganglion-cells. 

TJie  Functions  of  the  Spinal  Cord. 

The  functions  of  the  spinal  cord  may  be  described  under 
three  headings — viz.,  reflexion,  conduction,  and  transfer- 
ence. 

The  central  functions  of  the  spinal  cord  are  those  of  a 
reflex  centre. 

The  centrifugal  fibres  of  the  cord  do  not  conduct  volun- 
tary impressions  alone,  but  also  those  which  are  conducted 
to  the  cord  from  the  periphery  by  a  centripetal  or  sensory 
nerve  to  a  centre  in  the  cord,  and  which  are  then  reflected 
or  transmitted  from  this  centre  to  the  centrifugal  fibres. 
Motions  and  functions  so  produced  are  involuntary;  they 
are  produced  unconsciously  and  are  called  the  reflex  mo- 
tions or  acts.  Many  centres  in  the  cord  possess  the  prop- 
erty of  transferring  impressions  received  in  this  manner  to 
centrifugal  nerves.  We  distinguish  three  varieties  of  re- 
flex motions — viz. :  1.  Single  reflex  motions,  consisting  of 
a  single  muscular  contraction  as  the  result  of  a  peripheral 
irritation  of  a  sensory  nerve.     An  example  is  the  sudden 


THE    SPIXAL   COED.  425 

contraction  of  the  biceps  muscle,  caused  by  a  blow  on  the 
arm  over  the  region  of  this  muscle. 

2.  Extensive  non-co-ordinated  reflex  motions.  These  are 
tonic  or  tetanic  convulsive  contractions  of  one  or  several 
groups  of  muscles.  The  contractions  are  characterized  by 
being  purposeless  and  non  co  ordinated.  Such  convulsive 
reflex  motious  are  caused  by  an  excessive  irritation  of  the 
spinal  cord.  Certain  drugs,  such  as  strychnine,  nicotine, 
etc.,  when  given  in  large  doses,  increase  the  irritabihty  of 
the  spinal  cord,  so  that  the  least  irritation  of  the  skin 
excites  the  most  violent  convulsive  reflex  motions. 

3.  Co-ordinated  reflex  motions  are  those  in  which  mus- 
cular contractions  of  certain  muscle  groups  are  produced, 
caused  by  the  peripheral  irritation  of  a  sensory  nerve,  and 
resulting  in  motions  which  ordinarily  are  produced  by  an 
effort  of  the  wiU  and  with  a  certain  purpose. 

The  reflex  activity  of  the  spinal  cord  is  best  demonstrated 
when  it  is  severed  from  the  brain.  Cold-blooded  animals — 
for  example,  frogs — are  used  for  this  demonstration,  be- 
cause in  them  the  spinal  cord  retains  its  reflex  activity 
longer  than  in  warm-blooded  animals.  If  the  spinal  cord 
is  severed  from  the  brain  there  will  be  a  loss  of  voluntary 
motor  power  and  loss  of  sensation  below  the  point  of  sec- 
tion. If  a  frog  is  decapitated  it  is  unable  to  make  any 
voluntary  motions:  but  if  its  skin  is  touched  it  will  make 
the  most  comphcated  motions,  such  as  hopping,  drawing 
up  the  legs,  etc.  The  various  motions  which  we  make 
during  sleep — such  as  rolling  over,  scratching  where  the 
skin  is  irritated,  the  closing  of  the  palm  of  the  hand  or 
drawing  up  of  the  foot  when  tickled — are  all  voluntary 
motions  performed  during  unconsciousness. 

The  spinal  cord  is,  furthermore,  the  seat  of  a  number  of 
reflex  centres  which  preside  over  certain  functions  of  the 
body. 

These  special  reflex  centres  in  the  cord  are : 

1.  A  centre  for  the  dilatation  of  the  pupils;  this  is  located 


436      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

in  the  dorsal  region  between  the  first  and  second  dorsal 
vertebrae.  The  centripetal  fibres  are  contained  in  the  optic 
nerve,  the  centrifugal  fibres  in  the  cervical  portion  of  the 
sympathetic. 

2.  The  centre  of  micturition. 

3.  The  centre  of  defecation. 

4.  The  centre  for  the  erection  of  the  penis. 

5.  The  centre  for  the  ejaculation  of  the  semen. 

6.  The  centre  for  the  act  of  labor. 

7.  The  centre  for  the  secretion  of  sweat. 

8.  Vasomotor  and  vasodilator  centres. 

These  centres  are  located  in  various  parts  of  the  spinal 
cord,  and,  although  they  retain  their  activity  after  section 
of  the  cord,  they  are  normally  governed  by  centres  in  the 
medulla  and  must  therefore  be  considered  as  centres  sub- 
ordinate to  those  of  the  medulla. 

Many  refiex  motions  may  be  suppressed  by  an  effort  of 
the  will — for  instance,  the  closing  of  the  eye  when  the  eye- 
ball is  touched,  the  reflex  motions  produced  as  the  result 
of  an  irritation  of  the  skin,  etc.  This  voluntary  inhibition 
of  reflex  motions  is,  however,  limited.  No  reflex  motions 
can  be  suppressed  by  an  effort  of  the  will  which  ordinarily 
cannot  be  voluntarily  produced;  again,  many  reflex  mo- 
tions, such  as  ejaculation  of  semen,  the  motions  of  the 
iris,  the  act  of  labor,  etc.,  cannot  be  suppressed  by  an  effort 
of  the  will.  According  to  certain  authors  there  exists  in 
the  brain  an  automatic  inhibitory  centre  which  governs  the 
reflex  irritability  of  the  cord. 

Excessive  irritation  of  a  centripetal  or  sensory  nerve 
suppresses  reflex  motion. 

The  reflex  irritability  of  the  spinal  cord  may  also  be  in- 
creased or  decreased  by  certain  drugs;  among  these  are 
strychnine  and  nicotine,  which  increase,  and  chloroform, 
morphine,  and  bromides,  which  decrease  the  same. 

The  importance  of  the  spinal  cord  as  an  organ  of  con- 
duction has  already  been  demonstrated  by  its  structure 


THE    SPINAL   CORD.  427 

and  anatomical  relation.  All  impulses  from  the  periphery 
to  the  centres  in  the  cord,  medulla,  or  other  parts  of  the 
brain,  and  from  these  centres  to  the  periphery,  are  con- 
ducted through  the  various  parts  of  the  spinal  cord  in  such 
-a  manner  that  certain  parts  always  conduct  the  same  kind 
of  impressions. 

The  experiments  of  Brown- Sequard  and  others  regard- 
ing the  conduction  of  various  impressions  in  the  cord  have 
demonstrated  the  following: 

1.  Sensory  impressions  are  conveyed  to  the  cord  by  fibres 
of  the  posterior  roots  of  the  spinal  nerves,  and,  passing- 
through  the  posterior  columns  into  the  gray  substance, 
they  are  conducted  in  this  to  the  brain.  In  the  gray  sub- 
stance the  sensory  impressions  are  conducted  upward  on 
the  side  at  which  they  enter  for  a  short  distance  only,  and 
then  decussate  to  the  other  side,  to  be  conducted  to  the 
T3rain.  Section  or  disease  of  one  posterior  half  of  the  cord 
"is  followed  by  a  loss  of  sensation  on  the  opposite  side  of 
the  body. 

2.  Voluntary  motor  impulses  originate  in  the  brain  and 
are  conducted  along  the  fibres  of  the  superficial  layer  of 
the  crura  cerebri  and  along  the  longitudinal  fibres  of  the 
pons  to  the  pyramids  of  the  medulla.  In  the  anterior 
part  of  the  meduUa  there  takes  place  a  decussation  of  the 
voluntary  motor  impulses.  They  are  then  conducted  down- 
ward in  bundles  of  the  anterior  and  lateral  columns  of  the 
•spinal  cord  in  the  opposite  half,  and  are  finally  conducted 
from  the  cord  by  the  fibres  of  the  anterior  roots  of  the 
spinal  nerves. 

The  decussation  of  the  motor  impulses  does  not  take 
place  in  the  cord,  but  in  the  medulla.  Section  or  disease 
•of  the  anterior  and  lateral  tracts  of  the  cord  on  one  side  is 
followed  by  paralysis  or  loss  of  voluntary  motor  power  on 
the  same  side  of  the  body  below  the  point  of  section.  The 
fact  that  section  of  the  anterior  and  lateral  tracts  of  the 
■cord  is  followed  only  by  temporary  paralysis  (provided  the 


428     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

section  does  not  include  the  gray  matter)  tends  to  show 
that  voluntary  motor  impressions  are  also  conducted  along: 
the  gray  matter  of  these  portions  of  the  cord. 

The  various  other  impressions — such  as  tactile  impres- 
sions, inhibitory  impressions,  and  the  impressions  of  tem- 
perature— are  conducted  in  separate  portions  of  the  cord; 
•they  all  undergo  decussation  in  the  cord. 

The  meaning  of  the  term  transference  of  impulses  I  have 
already  described  when  speaking  of  the  functions  of  the 
nerve-centres.  This  property  or  function  is  possessed  by 
many  of  the  ganglion-cells  or  centres  of  the  spinal  cord. 
For  example,  the  pain  felt  in  the  knee-joint  as  an  early 
symptom  of  disease  of  the  hip  joint,  is  due  to  the  transfer- 
ence of  a  sensory  impression  from  a  sensory  nerve  of  the 
hip-joint  to  one  of  the  knee-joint. 

The  normal  activity  of  the  spinal  cord  and  its  irrita- 
bility are  dependent  upon  a  normal  circulation. 


LEOTUEE    XLV. 

THE   SPINAL  NERVES. 

The  thirty-one  pairs  of  spinal  nerves  arise  from  the 
spinal  cord,  pass  through  openings  in  the  membranes  of 
the  cord,  and  leave  the  spinal  canal  through  the  interverte- 
bral foramina.  The  spinal  nerves  are  divided  into  cervical, 
dorsal,  lumbar,  and  sacral.  Each  spinal  nerve  arises  from 
the  cord  in  two  roots — an  anterior  and  a  posterior. 

The  anterior  root  arises  from  the  antero-lateral  fissure, 
the  posterior  root  from  the  posterolateral  fissure,  of  the 
€ord, 

Charles  Bell  detected  in  1811  that  the  anterior  root  con- 
sists of  centrifugal  or  motor  fibres,  and  that  the  posterior 
root  consists  of  centripetal  or  sensory  fibres. 

The  two  roots  emerge  through  separate  openings  in  the 
dura  mater.  In  the  intervertebral  canal  the  sensory  root 
presents  a  ganglion  immediately  behind  this ;  the  two 
roots  unite,  forming  a  mixed  nerve,  which,  as  such,  emerges 
through  the  intervertebral  foramen  and  divides  into  an 
anterior  and  posterior  branch,  each  of  which  contains  both 
sensory  and  motor  fibres. 

Magendie  found  in  1822  that  the  motor  root  of  the  spinal 
nerves  also  contains  sensory  fibres.  This  is  shown  by  the 
fact  that  stimulation  or  section  produces  pain.  This  is  due 
to  the  fact  that  fibres  from  the  sensory  root  pass  into  the 
motor  root  at  the  point  of  union  of  the  two,  and  then  pass 
centrally  in  the  motor  root.  If  the  sensory  root  is  cut,  then 
the  motor  root  loses  its  sensibility.  The  sensibility  of  the 
motor  root  is  termed  recurrent  sensibility.  Experimental 
section  of  the  roots  has  shown  the  following: 

1.  Section  of  the  anterior  or  motor  root  produces  (a)  pain 


430     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

at  the  moment  of  section,  due  to  the  recurrent  sensibiUty 
of  the  motor  root;  (6)  a  sudden  contraction  of  the  muscles 
suppHed  by  that  nerve,  caused  by  the  mechanical  irritation 
produced  by  the  section, 

2.  After  section  the  muscles  supplied  by  that  nerve  are 
paralyzed;  there  is  no  loss  of  sensation  or  sense  of  touch  in 
the  same  region. 

3.  -  Stimulation  of  the  peripheral  stump  produces  muscu- 
lar contraction  and  pain  for  some  time  after  section. 

4.  Stimulation  of  the  central  stump  is  not  followed  by  any 
results. 

5.  Section  of  the  posterior  or  sensory  root  produces  pain 
at  the  moment  of  section, 

6.  At  the  moment  of  section  a  reflex  motion  is  produced 
as  the  result  of  the  mechanical  irritation. 

7.  Section  of  this  root  is  followed  by  loss  of  sensation 
and  sense  of  touch  in  the  region  supplied  by  that  nerve, 
whereas  motor  power  remains  intact  in  that  region. 

8.  Irritation  of  the  peripheral  stump  has  no  result;  irri- 
tation of  the  central  stump  produces  pain  and  reflex  mo- 
tion. 

9.  The  peripheral  stump  of  the  nerve  degenerates  after 
section  of  its  root. 

10.  The  spinal  cord  is  the  nutritive  centre  for  the  motor 
root,  the  spinal  ganglion  for  the  sensory  root. 

The  anterior  roots  of  the  spinal  nerves  contain  the  fol- 
lowing centrifugal  fibres: 

1.  Motor  fibres  for  the  voluntary  striated  muscles  of  the 
trunk  and  the  extremities. 

2.  Motor  fibres  for  the  involuntary  non-striated  muscular 
fibres  of  certain  organs,  as,  for  example,  those  of  the 
uterus,  the  bladder,  etc. 

3.  Motor  fibres  for  the  muscular  fibres  of  the  blood-ves- 
sels— viz.,  vasocontractor  fibres. 

4.  Inhibitor^y  fibres  for  the  contraction  of  the  muscular 
fibres  of  the  blood-vessels — viz.,  the  vasodilator  fibres. 

5.  Secretory  fibres  for  the  sweat  glands. 


THE    SPINAL   NERVES.  431 

6.  Trophic  fibres. 

The  posterior  or  sensory  roots  contaii:  the  followiDg 
centripetal  fibres: 

1.  Sensory  fibres  for  the  internal  organs  and  the  skin  of 
the  body,  exclusive  of  the  anterior  part  of  the  head,  the 
face,  and  the  interior  of  the  head,  which  are  supplied  by 
cranial  nerves. 

2.  Nerves  for  the  sense  of  touch  for  the  skin  of  the  same 
region. 

The  fibres  from  the  sensory  roots  also  conduct,  from  the 
periphery  to  the  centre,  stimuli  Avhich  result  in  the  produc- 
tion of  reflex  motions. 

The  sensory  fibres  of  the  trunk  of  a  mixed  nerA^e  are  dis- 
tributed to  the  skin  of  that  region  the  muscles  of  which 
are  supplied  by  the  motor  fibres  from  the  same  trunk. 

The  course  of  the  fibres  of  the  roots  of  the  spinal  nerves 
in  the  cord  varies. 

The  fibres  of  the  anterior  roots  enter  the  cord  in  several 
bundles;  these  pass  horizontally  or  obliquely  toward  the 
anterior  horn  of  the  gray  matter.  Most  of  the  fibres  are 
continuous  with  the  poles  of  the  unipolar  ganghon-cells  in 
the  anterior  horn,  some  with  the  anterior,  some  with  the 
middle,  and  some  with  the  internal  group  of  the  ganglion- 
cells.  Again,  some  of  the  fibres  pass  to  the  gray  matter  of 
the  posterior  horn,  but  are  not  connected  with  the  ceUs 
there.  Another  bundle  of  fibres  passes  across  the  gray  com- 
missure to  the  anterior  cornu  on  the  opposite  side.  Some 
of  the  fibres  of  the  anterior  root  also  pass  directly  in  the 
lateral  column  of  the  cord  without  any  connection  with  the 
ganglion-cells  in  the  cornua. 

The  fibres  of  the  posterior  roots  enter  the  cord  and  pass 
to  the  gray  matter  of  the  posterior  horn,  in  which  the 
axis-cylinder  of  the  fibres  breaks  into  several  branches, 
which  surround  the  ganglion-cells. 

THE   SYMPATHETIC   ISTIRVOUS   SYSTEM. 

The  sympathetic  nervous  system  is  distributed  all  over 


432     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

the  body;  it  contains  numerous  ganglia  and  communicates 
with  the  nerves  and  central  organs  of  the  cerebro-spinal 
nervous  system.  The  trunk  of  the  sympathetic  consists  of 
a  connected  chain  of  ganglia  placed  at  either  side  of  the 
spinal  column;  this  pre-vertebral  chain  of  ganglia  com- 
municates by  nerve-fibres,  called  the  rami  commimicantes, 
with  the  roots  of  the  spinal  nerves. 

From  each  ganglion  a  ramus  communicans  passes 
toward  the  point  of  union  of  the  roots  of  a  spinal  nerve. 
The  ramus  communicans  contains  both  centripetal  and 
centrifugal  fibres. 

From  the  pre-vertebral  chain  of  the  sympathetic  ganglia 
larger  trunks  pass  into  the  thoracic  and  abdominal  cavities, 
forming  there  plexuses  containing  numerous  ganglia;  and 
from  these  plexuses  fibres  are  distributed  to  the  various 
organs. 

The  function  of  the  ganglia  of  the  sympathetic  nervous 
system  is  principally  that  of  trophic  centres.  Some  ganglia 
are,  however,  the  p)hy si ological  centres  for  the  nerves  aris- 
ing from  them.  Such  ganglia  are,  for  instance,  the  auto- 
matic ganglia  of  the  heart,  the  ganglia  of  the  mesenteric 
plexus  of  the  intestines,  of  the  uterine  plexus,  etc.  The 
activity  of  these  ganglia  is  independent  of  any  nerve  con- 
nection with  the  cerebro-spinal  system.  The  functions  of 
these  ganglia,  and  of  the  nerves  connected  with  them,  will 
continue  even  if  all  connections  with  the  cerebro-spinal 
system  are  severed. 

Ordinarily  the  activity  of  these  independent  ganglia  is 
influenced  by  inhibitory  or  accelerating  impulses  received 
through  fibres  from  the  cerebro-spinal  system.  Many 
ganglia  are  reflex  ceyitres  which  reflect  stimuli  received 
from  the  periphery  to  the  centrifugal  fibres,  thus  produc- 
ing a  reflex  act. 

The  function  of  many  fibres  of  the  sympathetic  system 
depends  upon  their  connection  with  the  cerebro-spinal 
system. 


THE    SPINAL    XERYES.  433 

The  function  of  the  fibres  of  the  sympathetic  nervous 
system  is  the  same  as  that  of  all  other  nerve-fibres — viz., 
the  conduction  of  impulses — and,  according  to  the  charac- 
ter of  the  impulse  they  convey,  the  sympathetic  nerve- 
fibres  may  be  classified  into  sensory  fibres,  motor  fibres, 
secretory  fibres,  inhibitory  fibres,  trophic  fibres. 

The  sensory  fibres  are  distributed  to  the  internal  organs. 
Ordinarily  we  do  not  perceive  the  processes  taking  place  in 
these  organs.  We,  for  instance,  do  not  feel  the  moving  of 
the  ingesta  in  the  alimentary  canal,  the  walls  of  which  are 
supplied  by  sensory  fibres  from  the  sympathetic.  If,  how- 
ever, these  sensory  nerves  are  abnormally  irritated,  an 
increased  peristalsis  and  pain  are  produced,  which  shows 
that  these  sensory  fibres  are  in  connection  with  the  cerebral 
psycho-sensorial  centres.  The  fact  that  ordinary  physi- 
ological irritation  of  the  sensory  fibres  of  the  sympathetic 
does  not  produce  the  sensation  of  touch,  is  due  to  the  fact 
that  these  nerves  are  not  supplied  with  sensory  terminal 
apparatus  like  the  sensory  nerves  of  the  cerebro- spinal 
system. 

The  motor  fibres  are  distributed  only  to  iuvoluntary 
fibres — viz.,  to  the  muscular  fibres  of  the  heart,  the  blood- 
vessels, the  stomach  and  intestinal  canal,  and  many  inter- 
nal organs. 

The  motor  fibres  are  therefore  not  in  direct  connection 
with  the  psycho-motorial  centres.  There  exists,  however, 
a  certain  influence  of  the  cerebrum  upon  the  motor  func- 
tions of  the  sympathetic;  this  is  best  shown  by  the  effect 
of  certain  psychical  events,  such  as  fear,  shock,  fright, 
etc.,  upon  the  heart,  blood-vessels,  intestinal  canal,  etc. 

The  secretory  fibres  of  the  sympathetic  are  distributed  to 
many  secreting  glands — for  example,  to  the  salivary  glands 
and  to  the  secreting  glands  of  the  alimentary  canal. 

The  sympathetic  contains  fibres  which  conduct  inhibi- 
tory impulses  from  the  periphery  to  the  centre,  and  those 
which  convey  inhibitory  impulses  from  the  centre  to  the 

28 


434     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

periphery,  A  sudden  irritation  of  the  ahdominal  sympa- 
thetic produces,  by  i-eflex,  a  cessation  of  the  heart's  action. 
The  activity  of  the  fibres  of  the  sympathetic  is  induced 
either  by  reflex  action  or  by  the  automatic  activity  of  their 
gangUa. 

QUESTIONS   AND   EXERCISES. 

Subject. — The  Physiology  of  the  Xervous  System. 
Lectures  XXXIV.-XLV.  inclusive. 

679.  Name  the  divisions  of  the  nervous  system. 
6S0.  Name  the  organs  composing  the  cerebro-spinal  and 
those  composing  the  sympathetic  nervous  system. 

681.  Describe  the  structure  of  nerve-cells. 

682.  Give  the  distribution  and  structure  of  the  gray 
nerve-substance. 

683.  Name  the  various  kinds  of  nerve-centres,  their  dis- 
tribution, general  structure,  and  their  general  properties 
and  functions. 

684.  What  is  a  reflex  act  ? 

685.  How  are  the  centres  classified  in  accordance  with 
their  special  functions  ? 

686.  What  do  you  understand  by  simple  and  what  by 
co-ordinated  reflex  motions  ?     Give  an  example  of  each. 

687.  Explain  what  you  understand  by  the  automatic, 
reflex,  voluntary  activity  of  a  nerve-centre. 

688.  Give  the  general  structure  of  a  nerve-trunk. 

689.  Describe  the  structure  of  a  medullated  and  a  non- 
medullated  nerve-fibre. 

690.  Give  the  general  properties  and  functions  of  nerve- 
fibres. 

691.  Give  the  laws  regulating  the  conduction  of  impulses 
through  nerve-fibres. 

692.  What  is  the  rapidity  with  which  an  impulse  is  es- 
timated to  be  conducted  through  nerve-fibre  in  the  human 
subject  ? 


QUESTIONS   AND   EXERCISES.  435 

693.  What  is  the  cause  of  nerve  activity  ? 

694.  What  do  you  understand  by  nervous  irritability  ? 

695.  What  is  the  effect  of  the  apphcation  of  artificial 
stimuH  to  nerves  ? 

696.  Give  the  chemical  properties  and  composition  of 
nerve-tissue,  and  name  the  princijjal  products  of  the  retro- 
gressive metamorphosis  in  nerve-tissue. 

697.  How  is  the  nutrition,  growth,  and  regeneration  of 
nerve  tissue  maintained  ? 

698.  Name  the  parts  which  compose  the  brain. 

699.  Name  the  membranes  of  the  brain  and  their  uses. 

700.  What  is  the  weight  of  the  human  brain  ? 

701.  What  is  the  cerebrum?  Name  its  lobes  and  fis- 
sures. 

702.  What  are  the  sulci,  and  what  do  they  indicate  ? 
70.'^.  Name  the  principal  anatomical  points  on  the  under 

surface  of  the  cerebrum. 

704.  Name  the  basal  ganglia  of  the  brain. 

70.5.  Describe  the  distribution  of  white  and  gray  nerve- 
substance  in  the  cerebrum. 

706.  What  is  the  function  of  the  gray  cortical  substance 
of  the  cerebrum  ? 

707.  What  is  the  function  of  the  white  matter  of  the 
cerebrum  ? 

708  Define  the  psycho-motorial,  the  psycho-sensorial, 
the  psycho-acQustic,  and  the  psycho-visual  areas  on  the 
cortical  gray  substance  of  the  cerebrum. 

709.  Describe  and  give  the  functions  of  the  corpora 
striata;  thalami  optici;  corpora  quadrigemina. 

710.  What  w-ould  be  the  effect  of  pressure  upon,  or  de- 
struction of,  the  psycho-motorial  area  on  one  side  of  the 
cerebrum  { 

711.  Give  the  boundaries  of  the  fifth,  the  lateral,  and  the 
third  ventricles  of  the  brain. 

712.  Name  the  boundaries  of,  and  the  parts  contained  in, 
the  interpeduncular  space. 


436     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

713.  What  is  the  corpus  callosum  ?  the  fornix  ?  the  veluin 
interpositum  ? 

714.  Give  the  location,  the  cross-structure,  and  the  func- 
tions of  the  cerebellum. 

715.  Name  the  peduncles  of  the  cerebellum. 

716.  Give  the  cross  structure  and  functions  of  the  pon& 
Varolii. 

717.  Give  the  structure  of  the  crura  cerebri  and  their 
functions. 

718.  Give  the  anatomy  and  structure  of  the  medulla  ob- 
longata. 

719.  Give  the  functions  of  the  medulla. 

720.  Name  the  more  important  centres  located  in  the  me- 
dulla. 

721.  Give  the  cross-anatomy  and  the  structure  of  the 
spinal  cord. 

722.  Name  some  of  the  more  important  centres  of  the 
spinal  cord. 

723.  Name  the  twelve  pairs  of  cranial  nerves,  and  give 
their  superficial  and  deep  origins,  their  functions  and  gene- 
ral distribution. 

724.  Give  the  number  and  classification  of  the  spinal 
nerves. 

725.  Describe  the  origin  and  general  arrangement  of  the 
spinal  nerves. 

726.  Give  the  course  of  a  sensory  impulse  from  the  hand 
to  the  brain,  and  the  course  of  a  voluntary  motor  impulse 
from  the  brain  to  the  hand. 

727.  Give  the  general  arrangement  of  the  sympathetic 
nervous  system. 

728.  Describe  the  nervous  mechanism  of  the  acts  of  deg- 
lutition, defecation,  and  micturition. 

729.  What  do  you  understand  by  paralysis,  anassthesia, 
cretinism,  and  coma  ? 


LEGTUHE  XLVL 

THE   SENSES   AND   THE   SENSORY   ORGANS. 

The  animal  body  is  provided  with  certain  organs  and 
mechanisms  by  which  the  mind,  through  the  medium  of 
the  nervous  system,  perceives  the  various  occurrences  in 
the  external  world  and  any  changes  in  the  body. 

The  mind  perceives  these  various  sensory  impressions  as 
the  result  of  the  stimulation  of  psycho-sensorial  centres  in 
the  cerebrum.  These  centres  have  each  a  special  function, 
so  that  through  the  activity  of  such  a  centre  the  mind  per- 
ceives sensory  impressions  of  one  kind;  again,  these  centres 
are  ordinarily  stimulated  by  impressions  conducted  to  them 
by  special  nerves. 

The  various  sensory  impressions  which  the  mind  thus 
perceives  may  be  classified  into  special  and  general. 

General  or  common  sensations  are  those  by  which  the 
mind  recognizes  changed  conditions  of  the  body. 

The  sensations  of  hunger,  thirst,  fatigue,  discomfort,  dis- 
gust, satiety,  the  sensation  producing  the  desire  to  defe- 
cate or  urinate,  and  the  sensation  of  itching  d^ndi  burning  of 
the  skin — all  these  are  considered  as  common  sensations. 

Special  sensations  are  those  by  which  the  mind  perceives 
occurrences  in  the  external  world,  as,  for  instance,  sights, 
sounds,  the  character,  size,  form,  and  consistency  of  various 
objects,  etc. 

These  special  sensations  we  perceive  through  the  medium 
of  specially  constructed  organs,  which  are  called  the  organs 
of  special  sense,  as,  for  instance,  the  eye,  the  ear,  etc. 
We  distinguish  five  special  senses:  touch,  smell,  taste, 
hearing,  and  sight. 


438     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  Special  Sense  of  Touch. 

By  the  contact  of  the  skin  and  certain  portions  of  the 
mucous  membrane  with  various  objects,  certain  sensations 
are  produced,  which  are  described  as  feehng. 

These  sensations  may  be  of  two  kinds — viz.,  the  sensa- 
tion of  touch,  or  the  tactile  sense,  and  the  sensation  of  ther- 
mal conditions,  or  tempemture  sense.  Tlirough  the  former 
we  perceive  mechanical  irritations  of  the  skin,  the  charac- 
ter, form,  and  size  of  objects  coming  in  contact  with  the 
skin,  and  by  it  we  canlocaHze  the  irritation.  Through  the 
temperature  sense  we  perceive  whether  an  object  which 
touches  the  body  is  warmer  or  colder  than  the  skin. 

The  tactile  and  the  temperature  senses  are  distributed  all 
over  the  skin,  and  extend  over  certain  parts  of  the  mucous 
membrane— viz.,  over  that  of  the  lips,  the  tongue,  the  buc- 
cal cavity,  and  the  nose;  the  tactile  and  temperature  senses 
are  restricted  to  these  regions.  Mechanical  or  thermal 
irritation  of  internal  organs  produces  painful  sensations, 
but  not  the  sensation  of  touch  or  temperature. 

The  apparatus  and  mechanism  through  which  we  per- 
ceive the  sensations  of  touch  and  temperature  are  the  per- 
ipheral terminals  of  the  sensory  nerves  of  the  skin,  and  of 
the  mucous  membrane  of  the  regions  mentioned. 

The  sensory  nerves  of  the  skin  terminate  in  the  subcu- 
taneous cellular  layer,  in  the  cutis  vera,  and  in  the  stratum 
mucosum  of  the  epidermis. 

The  following  peripheral  terminations  of  the  nerves  of 
the  skin  are  known  as: 

1.  The  end-bulbs  of  Krause. 

2.  The  tactile  corpuscles. 

3.  The  Pacinian  corpuscles. 

4.  Tactile  cells. 

5.  Termination  of  fibrillae. 

1.  The  end-bulbs  of  Krause  are  minute,  oblong,  rounded 
bodies,  consisting  of  a  fine  capsule  which  is  filled  with  a 


THE    SENSES   AND   THE    SENSORY    ORGANS.  439 

homogeueous  substance  and  contains  the  axis-cylinder  of  a 
nerve-fibre;  this  terminates  in  a  button-shaped  expansion 
or  in  a  spiral- shaped  plexus. 

End-bulbs  of  Krause  are  contained  in  the  mucous  mem- 
brane of  the  lips,  tongue,  nose,  also  in  the  conjunctiva;  in 
the  skin  they  are  contained  in  the  upper  layers  of  the 
corium,  or  cutis  vera,  and  in  the  papillae. 

2.  The  tactile  corpuscles  are  contained  principally  in  the 
papillae  of  the  skin  of  the  soles  of  the  feet  and  the  palms 
of  the  hands.  The  tactile  corpuscles  are  oblong,  egg- 
shaped  bodies  which  fill  the  papillae;  they  consist  of  a 
connective-tissue  capsule  traversed  by  delicate,  imperfect 
septa  ;  the  axis-cylinder  of  a  nerve- fibre  enters  the  cap- 
sule and  divides  into  several  delicate  branches,  which 
pursue  a  spiral  course  and  terminate  near  the  periphery  of 
the  capsule  in  fine,  bulbous  expansions. 

Tactile  corpuscles  are  found  only  in  the  papillge  of  the 
skin  of  those  regions  which  are  most  sensitive. 

3.  The  Pacinian  corpuscles  are  large,  egg-shaped  bodies, 
1  to  4  millimetres  in  length,  consisting  of  a  number  of 
connective-tissue  lamellae  which  enclose  a  space  which  is 
lined  by  a  single  layer  of  nucleated  endothelial  cells  and  is 
filled  with  a  homogeneous  transparent  substance. 

The  axis-cylinder  of  a  single  nerve-fibre  enters  this 
space  and  terminates  near  the  periphery  in  a  rounded 
knob.  Sometimes  the  fibres  bifurcate.  Such  Pacinian 
corpuscles  are  found  in  the  subcutaneous  cellular  tissue  of 
the  skin  of  the  soles  of  the  feet  and  palms  of  the  hands; 
they  are  also  found  on  the  terminations  of  the  sensory 
nerves  of  the  joints.  On  account  of  their  deep  locations 
these  corpuscles  cannot  be  considered  as  organs  of  touch, 
but  are  probably  the  organs  by  w^hich  we  perceive  the 
sensations  of  tension  and  motion. 

4.  The  tactile  cells  are  epithelial  cells  in  which,  or  be- 
tween which,  the  primitive  fibrillse  of  a  nerve-fibre 
terminate.     This  form  of  nerve -termination  is  found  in 


440     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

certain  parts  of  the  skin  and  mucous  membrane  and  in 
the  anterior  epithelium  of  the  cornea. 

As  I  have  stated  before,  through  these  peripheral  nerve- 
termini  we  perceive  the  sensation  of  touch;  we  are  able  to 
locaUze  the  touching  object  and  to  distinguish  its  charac- 
ter and  form:  furthermore,  we  are  enabled  to  distinguish 
thermal  changes. 

An  important  question  which  here  arises  is  whether  the 
organs  for  the  sensation  of  touch  and  for  temperature  sen- 
sation are  the  same,  or  whether  special  nerves  or  special 
peripheral  nerve-terminations  exist  for  each  of  the  two 
sensations.  Certain  pathological  observations,  and  the  fact 
that  the  two  sensations  are  unequally  distributed  over  the 
skin,  tend  to  sustain  the  latter  view.  It  has  also  been  ob- 
served in  certain  pathological  lesions  that  the  sense  of 
touch  is  totally  absent  while  the  temperature  sense  still 
exists,  and  vice  versa. 

Abnormally  strong  irritation  of  the  skin  produces  a  pain- 
ful sensation,  and  again  the  question  arises  whether  this 
sensation  is  produced  by  the  abnormal  irritation  of  the 
touch  and  temperature  sensory  organs,  or  by  the  irritation 
of  special  sensory  nerves. 

We  must  accept  the  former  theory  as  the  more  probable, 
because  the  irritation  of  other  nerves  or  organs  of  special 
sense  does  not  produce  pain;  also  because  the  mechani- 
cal irritation  of  all  organs  which  are  supplied  with  sensory 
nerves  produces  pain,  although  these  organs  are  not  pro- 
vided with  the  described  peripheral  terminal  apparatus  of 
the  nerves  of  the  skin.  Pathological  observations  also  sus- 
tain this  theory.  In  analgesia — viz.,  loss  of  painful  sensa- 
tion—a part  of  the  sense  of  touch  and  temperature  may 
exist  undisturbed.  We  also  know  that  tactile  and  thermal 
impressions  are  conducted  in  different  portions  of  the  cord, 
from  the  general  sensory  impressions. 

By  the  temperature  sense  of  the  skin  we  perceive  the 
sensations  of  warmth  and  cold.     We  are  therefore  able  to 


TEE    SENSES   AND    THE    SENSORY   ORGANS.  4:41 

determine  the  exact  degree  of  warmth  of  ao  object  with 
which  we  come  in  contact.  Experiments  have  shown  that 
the  temperature  sense  is  differently  developed  in  the  va- 
rious regions  ;  the  tip  of  the  tongue  is  probably  the  most 
sensitive  location  in  this  respect.  Very  high  and  very 
low  temperatures  produce  pain  and  temporarily  decrease 
the  temperature  sense. 

The  fact  is  peculiar  that  if  two  portions  of  the  skin 
which  have  an  unequal  temperature  come  in  contact,  the 
sensation  of  cold  is  perceived  iirst;  as  a  rule,  however,  it 
may  be  said  that  that  temperature  is  perceived  first  which 
diverges  mostly  from  the  temperature  of  the  skin. 

The  touch  and  temperature  senses  are  destroyed  in  those 
parts  of  the  surface  of  the  body  where  the  skin  is  destroyed 
or  removed. 

The  Special  Sense  of  Taste. 

The  seat  of  this  sense  is  the  mucous  membrane  of  the 
tongue,  the  soft  palate,  the  uvula,  and  the  tonsils.  The 
sense  of  taste  is  the  result  of  the  irritation  of  the  periphe- 
ral termini  of  the  glosso-pharyngeal  nerves,  by  which  the 
impressions  are  conducted  to  a  special  centre  in  the  brain. 
The  trifacial  nerve,  through  its  lingual  branch,  is  also  said  to 
conduct  impressions  of  this  kind.  It  is,  however,  very  likely 
that  this  nerve  receives  its  fibres  which  conduct  these  im- 
pressions, through  its  various  communications,  from  the 
glosso-pharyngeal  nerve. 

The  tongue,  which  is  the  principal  seat  of  the  sense  of 
taste,  is  composed  of  extrinsic  and  intrinsic  muscles,  and  is 
covered  with  mucous  membrane  which  contains  numerous 
minute  glands  and  follicles.  The  mucous  membrane  of  the 
tongue  consists  of  a  layer  of  connective  tissue,  called  the 
corium  or  mucosa,  from  which  are  projected  numerous 
•cone-shaped  elevations  called  the  papillce:  these,  like  the 
-whole  corium,  are  covered  with  scaly,  stratified  epithelium. 

The  papillae  contain  the  delicate  organs  of  the  sense  of 


443     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTO»LOGy. 

taste.  We  distinguish  three  kinds  of  such  papillae:  the 
papillae  circumvallatae,  the  papillae  fungiformes,  and  the 
papilla3  filiformes;  they  all  differ  in  structure  and  location. 

The  circumvallate  papillcB,  or  jjapillce  maxima!,  8  to  12  in 
number,  are  arranged  in  two  diverging  rows.  Each  pa- 
pilla consists  of  a  cone-like  projection  from  a  depression  in> 
the  mucous  membrane  in  the  back  part  of  the  dorsum  of 
the  tongue,  near  its  base.  The  papilla  is  surrounded  by  a 
shallow  depression  ;  it  is  narrow  at  its  base  and  wider 
at  its  free  end.  Projecting  from  its  surface  are  numerous 
minor  or  secondary  papillae;  the  surface  of  the  papilla  is 
made  smooth  by  the  epithelium  covering  it. 

The  fungiform  papillcE  are  found  principally  at  the  sides 
and  tip  of  the  tongue;  they  are  more  numerous  than  the 
former;  they  are  rounded  projections  from  the  mucous 
membrane,  are  broader  at  their  free  end  than  at  their  at- 
tached base,  and  also  present  secondary  papillae;  their  sur- 
face is  covered  by  a  thin  epithelial  layer  and  has  a  dark- 
red  color. 

The  filiform  papillce  are  distributed  principally  over  the- 
mid-portion  of  the  dorsum  of  the  tongue;  they  are  smaller, 
cone  shaped  elevations,  from  the  apices  of  which  are  pro- 
jected fine,  fihform  processes  or  secondary  papillae. 

Besides  these  three  characteristic  forms  the  mucous  mem- 
brane also  presents  numerous  simple papillcB  which  resemble- 
those  of  the  corium  of  the  skin,  and  consist  of  a  cone-like 
elevation  which  is  covered  with  epithelium  and  contains, 
in  its  interior  a  capillary  network. 

The  structure  of  the  papillae  of  the  tongue  resembles  that 
of  the  papillae  of  the  corium  of  the  skin.  They  are  eleva- 
tions frorli  the  surface  of  the  mucosa  or  the  corium  of  the 
mucous  membrane ;  they  are  covered  with  epithelial  cells 
and  contain  capillai'ies  and  nerve- terminals;  they  differ 
in  structure  from  the  papillae  of  the  skin,  in  that  they  pre- 
sent secondary  papillae  and  in  that  the  nerve-termini  differ. 

In  the  circum vallate  papillae  and  in  the   fungiform  these 


THE   SENSES    AND   THE   SENSORY    ORGANS.  443 

nerve-terminals  are  very  abundant  and  consist  of  a  plexus 
of  large  nerve -fibrillae.  The  mode  of  nerve-termination  in 
the  filiform  papillae  is  not  fully  known. 

In  the  epithelium  covering  the  circumvallate  and  many 
of  the  fungiform  papillae  are  situated  numerous  pecuharly 
constructed  bodies  v^hich  are  known  as  taste-goblets  ;  these 
are  oblong,  rounded  bodies  which  are  attached  by  oue  end 
to  the  coriuni  of  the  mucous  membrane,  while  the  other 
end  presents  minute  openings  which  open  between  the  epi- 
thelial cells.  Their  walls  are  composed  of  two  kinds  of 
cells  :  the  outer,  or  cortical  layer,  consists  of  elongated 
cells  which  are  connected  at  their  edges  ;  the  inner  layer 
consists  of  long,  nucleated,  spindle-shaped  cells  called  the 
gustatory  cells.  The  fibres  of  the  glosso-pharyngeal  nerve 
enter  the  taste-goblets  at  their  base,  terminating  in  them 
in  a  fine,  fibrillar  plexus,  the  fibres  of  which  are,  however, 
not  connected  with  the  taste-cells. 

Through  the  sense  of  taste  w^e  differentiate  between  the 
various  qualities  of  the  sensation  ;  we  perceive  a  sweet, 
sour,  bitter,  alkaline,  or  sahne  taste.  The  various  portions 
of  the  tongue  are  unequally  endowed  with  the  sense  of 
taste  ;  it  is  distributed  only  to  the  tip,  the  posterior  part 
of  the  dorsum,  and  in  part  to  the  sides  of  the  tongue. 
Again,  the  sense  for  distinguishing  between  different  quali- 
ties of  taste  is  not  the  same  in  all  parts  of  the  tongue. 
Thus  we  find  that  a  bitter  taste  is  principally  distinguished 
by  the  back  part  of  the  dorsum,  and  sour  and  sweet  tastes 
are  recognized  by  the  tip  of  the  tongue. 

The  many  variations  of  taste  are  due  to  the  fact  that  the 
taste  sensations  are  accompanied,  first,  by  the  sensation  of 
touch,  produced  by  its  coming  in  contact  with  the  organs  of 
touch  ;  second,  by  those  substances  which  we  taste  ;  and 
third,  by  the  sensation  of  smell  produced  by  the  tasting  of 
odoriferous  substances. 


LECTURE    XLVII. 

THE   SENSES   AND   THE   SENSORY  ORGANS    {continued). 

The  Sense  of  Smell. 

Through  the  sense  of  smell  the  mind  obtains  knowledge 
of  the  quality  of  the  various  odors  emanating  from  odor- 
iferous substances.  The  sensation  is  caused  by  the  stimu- 
lation of  the  terminals  of  the  olfactory  nerves.  The  im- 
pression is  conducted  by  the  olfactory  nerves,  which  are 
the  nerves  of  the  special  sense  of  smell,  to  the  centre  in  the 
brain  which  is  thus  stimulated,  and  the  activity  of  which 
causes  the  sensation  of  smell. 

The  mucous  membrane  of  the  upper  third  of  the  septum 
of  the  nose,  of  the  superior  turbinated  bones,  upper  part 
of  the  middle  turbinated  bones,  and  the  upper  part  of  the 
nasal  cavity  beneath  the  cribriform  plate  of  the  ethmoid,  is 
the  seat  of  the  sense  of  smell.  The  mucous  membrane 
covering  this  region  of  the  nasal  cavity  is  termed  the  ol- 
factory membrane.  It  is  covered  with  non-ciliated  columnar 
epithelial  cells,  and  scattered  between  these  are  found  pecu- 
liar fusiform  cells  which  are  called  the  olfactory  cells  ; 
they  have  projections  penetrating  into  the  depth,  and  it 
is  supposed  that  these  are  connected  with  the  terminals  of 
the  fibres  of  the  olfactory  nerves. 

An  essential  condition  for  the  sensation  of  smell  is  that 
we  inspire  air  through  the  nose.  If  we  breathe  through 
the  mouth  or  stop  breathing  we  do  not  smell.  The  sensa- 
tion of  smell  is  also  stronger  during  inspiration  than  dur- 
ing expiration.  The  sense  of  smell  is  exceedingly  acute  ; 
through  it  we  are  able  to  recognize  substances  in  smaller 
quantities  than  by  means  of  any  other  sense. 


THE    SENSES    AND    THE    SENSORY    ORGANS.  445 

Exactly  how  it  is  that  we  recognize  so  many  odors  has 
not  been  fully  explained.  It  is  not  likely  that  there  are 
special  fibres  and  termini  for  each  of  the  various  odors.  It 
is  more  likely  that  the  stimulation  of  the  peripheral  ter- 
mini is  due  to  a  chemical  influence  by  the  particles  of 
odoriferous  gases,  and  that  this  chemical  influence  varies 
with  the  different  substances,  thus  causing  the  various 
sensations  of  smell. 

Tlie  Sense  of  Hearing. 

Through  the  sense  of  hearing  the  mind  is  able  to  perceive 
the  various  sounds  and  their  character.  The  sensation  of 
sound  is  produced  through  the  irritation  of  the  peripheral 
terminals  of  the  auditory  nerve  in  the  inner  ear  by  tho 
sound-waves.  The  auditory  nerve  possesses  the  specific 
property  of  conducting  to  centres  in  the  brain  impulses 
which  result  in  the  sensation  of  hearing.  The  special  cen- 
tres are  located  in  the  cerebral  psycho  sensorial  area  of  the 
cortex.  Direct  stimulation  of  the  fibres  of  the  auditory 
nerve  does  not  produce  sensations  of  hearing ;  it  is  the 
nerve-terminations  in  the  middle  ear  which  are  stimulated 
by  sound.  Destruction  of  the  middle  ear  causes  total  deaf- 
ness on  the  respective  side. 

The  Organs  of  Hearing. — The  ear  consists  of  three  prin- 
cipal parts — viz.,  the  external  ear,  the  middle  ear  or  tympa- 
num, and  the  internal  ear  or  labyrinth. 

The  external  ear  consists  of  the  auricle  or  pinna  and  of 
the  meatus. 

The  auricle  or  pinna  is  the  outer  ear  ;  it  is  a  concave, 
oval  organ  attached  to  the  sides  of  the  head  ;  it  serves  to 
collect  the  vibrations  of  the  air  by  which  sound  is  pro- 
duced. 

The  organ  is  directed  with  the  convexity  of  its  border 
backward  and  with  its  concavity  forward  ;  at  its  bottom 
the  auricle  communicates  with  the  auditory  canal.  The 
auricle  is  composed  of  a  thin  plate  of  yellow  fibro-cartilage 


446    lb:ctures  ox  human  phtsiology  and  histology. 

and  of  ligaments  and  muscles  ;  its  surfaces  are  covered 
with  skin,  which  outside  is  continuous  with  that  of  the 
head,  and  inside  is  continuous  with  the  skin  hning  the  au- 
ditory canal. 

The  meatus  auditorius  exfei'uiis,  or  the  auditory  canal, 
is  a  Uttle  over  an  inch  long,  and  begins  by  a  funnel  shaped 
expansion  at  the  deepest  portion,  or  concha,  of  the  concav- 
ity of  the  auricle  ;  it  passes  inward  and  forward,  and  is 
bounded  internally  by  the  menibrana  tympani.  The  audi- 
tory canal  consists  in  its  external  third  of  cartilaginous, 
and  in  its  posterior  or  inner  two-thirds  of  osseous  walls.  The 
canal  is  constricted  at  its  mid-portion  and  expanded  at  its 
ends;  the  inner  opening  is  covered  with  the  membrana  tym- 
pani, which  is  a  round  membrane  composed  of  elastic 
fibres,  is  about  one- tenth  of  a  millimetre  thick,  and  is 
stretched  over  the  internal  opening  of  the  canal.  In  its 
centre  the  membrana  tympani  presents  a  funnel-shaped  in- 
dentation, which  is  produced  by  the  connection  of  the 
handle  of  the  malleus  with  the  internal  surface  of  the 
membrane. 

The  middle  ear,  or  tympanum,  is  an  irregular-shaped 
cavity  contained  in  the  petrous  portion  of  the  temporal 
bone  ;  its  outer  wall  is  formed  by  the  membrana  tympani, 
its  roof  and  floor  by  osseous  lamella3.  In  its  lower  portion 
the  tympanum  communicates  with  the  pharyngeal  cavity 
by  the  Eustachian  tube  :  its  inner  walls  are  formed  by  the 
bony  walls  of  the  labyrinth.  In  the  interior  of  the  tym- 
panum are  contained  the  three  ossicles,  called,  from  their 
shape,  the  malleus,  incus,  and  stapes,  which  are  connected 
with  the  membrana  tympani  and  the  labyrinth.  The  han- 
dle of  the  malleus  is  attached  to  the  inner  surface  of  the 
membrana  tympani  ;  its  head  is  connected  by  a  joint  with 
the  incus.  The  malleus  has,  at  the  junction  of  its  head 
with  the  handle,  two  processes.  The  long  process,  called 
iYie processus  foliaceus,  is  directed  forward  and  is  attached 
to  the  anterior  wall  of  the  tympanic  cavity  ;  the  other, 


THE    SENSES   AND    THE   SENSORY   ORGANS.  447 

the  sliort  process,  is  directed  toward  the  upper  border  of 
the  tympanic  membrane  ;  the  head  is  directed  upward, 
extending  over  the  upper  edge  of  the  tympanic  mem- 
brane. 

The  incus  resembles  somewhat  a  molar  tooth  with  two 
roots.  The  surface  of  the  body  of  the  incus,  which  would 
correspond  with  the  masticating  surface  of  the  crown  of 
the  molar  tooth,  articulates  with  the  head  of  the  malleus. 
Projecting  from  the  body  are  two  processes  resembling  the 
roots  of  a  tooth  ;  the  shorter  of  the  two  is  projected  hori- 
zontally backward  and  is  attached  to  the  posterior  wall  of 
the  tympanic  cavity  ;  the  longer  process  is  directed  down- 
ward, parallel  with  the  handle  of  the  malleus  ;  its  lower 
part  is  bent  a  little  inward  and  terminates  in  a  small  but- 
ton-shaped expansion  called  the  os  orhiculare,  which 
articulates  with  the  little  head  of  the  stapes.  The  foot 
portion  of  the  stapes  is  attached  to  the  membrane  which 
covers  the  fenestra  ovalis  in  the  inner  walls  of  the  tym- 
panic cavity. 

The  ossicles  in  the  tympanum  are  connected  with  each 
•other  and  with  the  walls  of  the  tympanum  by  fine  liga- 
ments, and  are  moved  by  two  small  muscles — viz.,  the  tensor 
tympani  and  the  stapediiis.  The  former,  by  its  contrac- 
tion, acts  upon  the  tympanic  membrane  ;  the  latter  is  at- 
tached to  the  head  of  the  malleus,  and  by  its  contractions 
draws  it  backward. 

The  cavity  of  the  tympanum  is  lined  with  mucous  mem- 
brane which  is  continuous  with  that  lining  the  pharynx, 
through  the  Eustachian  tube.  Inward  the  mucous  mem- 
brane of  the  tympanum  is  continuous  with  that  which 
lines  the  mastoid  cells  in  the  mastoid  portion  of  the  tem- 
poral bone.  The  mucous  membrane  covers  the  walls  of 
the  tympanum,  and  the  ossicles,  membranes,  and  muscles 
in  the  same  ;  it  is  covered  with  ciliated  epithelial  cells. 
The  cavity  of  the  tympanum  is  filled  with  air  through  the 
Eustachian  tube. 


448     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

3.  The  interned  ear,  or  labyrinth,  consists  of  the  osseous, 
and  the  membranous  labyrinth. 

{d)  The  osseous  labyrinth  is  a  complex  excavation  in  the 
interior  of  the  petrous  portion  of  the  temporal  bone,  inter- 
nal to  the  tympanum.  The  cavity  of  the  labyrinth  com- 
municates at  its  anterior  wall,  by  two  foramina,  with  the 
cavity  of  the  tympanum.  The  two  foramina — viz.,  the 
fenestra  ovalis  and  the  fenestra  rotunda — are  closed  by 
membranes  ;  to  that  covering  the  latter  foramen  is  at- 
tached the  foot-plate  of  the  stapes,  or  stirrup.  The  osseous 
labyrinth  consists  of  three  parts — viz.,  the  vestibule,  the 
semicircular  canals,  and  the  cochlea. 

The  vestibule  is  the  central  portion  of  the  cavity  of  the 
internal  ear. 

The  semicircular  canals  are  three  semicircular  excava- 
tions in  the  substance  of  the  bone,  posterior  to  the  central 
cavity,  or  vestibule,  with  which  the  canal  communicates. 
According  to  the  direction  in  which  these  canals  penetrate 
the  substance  of  the  bone,  they  are  called  the  superior, 
the  anterior,  and  the  posterior  semicircular  canal. 

The  cochlea  is  an  excavation  in  the  bone  anterior  to  the 
vestibule;  the  cochlea  resembles  the  interior  of  the  shell  of 
a  common  snail. 

(6)  The  membranous  labyrinth  is  a  closed  membranous 
canal  which  is  filled  with  a  fluid,  the  endolympli.  The 
membranous  labyrinth  is  attached  to  the  walls  of  the  ex- 
cavations of  the  three  portions  of  the  bony  labyrinth  To 
the  walls  of  the  membranous  labyrinth  are  distributed  the 
terminations  of  the  fibres  of  the  auditory  nerve.  External 
to  the  walls  of  the  membranous  labyrinth  is  a  collection  of 
fluid,  the  perilymph. 

The  auditory  nerve  enters  the  cavity  of  the  internal  ear 
through  the  meatus  auditorius  internus.  Entering  the 
labyrinth  or  internal  ear,  it  divides  into  two  branches — 
one  which  is  distributed  to  the  vestibule  and  semicircular 
canals;  the  other  is  distributed  to  the  cochlea.     The  exact 


THE   SENSES   AND    THE    SENSORY   ORGANS.  449 

mode  in  which  the  fibres  of  the  auditory  nerve  terminate 
is  not  known. 

The  function  of  the  compUcated  auditory  apparatus  is  to 
conduct  sound  to  the  terminals  of  the  auditory  nerve, 
which  are  thus  stimulated.  For  this  purpose  alone,  how- 
ever, the  auditory  apparatus  would  not  need  to  be  as  com- 
plicated as  it  is.  The  complex  structure  of  the  organ  has 
for  its  object  the  perfection  of  the  sonorous  vibrations,  and 
maintaining  as  much  as  possible  the  strength  and  charac- 
ter of  the  vibrations. 

The  vibrations  are  conducted  to  the  termini  of  the  audi- 
tory nerve  by  three  media — viz.,  by  the  air.  by  the  solid 
portions  of  the  auditory  apparatus,  and  by  the  liquid  in 
the  internal  ear. 

The  function  of  the  auricles  is  to  collect  the  vibrations. 
These  are  conducted  by  the  air  through  the  auditory  canal 
to  the  membrana  tympani;  the  vibrations  are  trans- 
mitted to  the  membrane  which  covers  the  fenestra  ovalis 
through  the  medium  of  the  chain  of  ossicles  in  the  middle 
ear;  the  vibrations  of  this  membrane  are  transmitted  by  the 
fluid  in  the  labyrinth  to  the  terminals  of  the  auditory 
nerve. 

This  fully  explains  the  functions  of  the  membrana  tym- 
pani, of  the  ossicles  in  the  middle  ear,  of  the  membrane 
covering  the  fenestra  ovalis,  and  of  the  fluid  in  the  laby- 
rinth. 

The  function  of  the  Eustachian  tube  is  to  maintain  an 
equal  density  between  the  air  in  the  tympanum  and  the 
external  air.  It  thus  prevents  the  effects  of  an  increased 
tension  of  the  tympanic  membrane. 

The  membrana  tympani  and  the  whole  auditory  appara- 
tus are  so  constructed  that  the  sonorous  vibrations,  which 
differ  in  number  and  strength  in  the  various  sounds,  are 
conducted  to  the  auditory  nerve  in  a  nearly  even  strength 
— which  tends  to  explain  why  the  mind  perceives  the  vari- 
ous sounds  as  such. 

29 


450     LECTURES  ON   HUMAN   PHYSIOLOGY    AND    HISTOLOG  Y. 

The  time  is  too  limited  to  say  aoything  on  the  subject  of 
acoustics  in  connection  with  the  sense  of  hearing.  I  have 
therefore  confined  myself  purely  to  the  physiology  of 
hearing. 


LEOTUEE   XLYIII. 

THE   SENSES   AND   THE   SENSORY  ORGANS   {continued). 

'Hie  Sense  of  Sight. 

The  organ  of  the  sense  of  sight  is  the  eye.  The  nerves 
for  the  special  sense  of  sight  is  the  optic  ;  the  terminal  ex- 
pansion of  this  nerve  into  the  retina  is  the  organ  by  whichs 
sight  is  perceived.  Light  is  conducted  to  the  retina  by  the- 
refracting  media  of  the  eye — viz.,  the  cornea,  the  aqueous- 
humor,  the  crystalline  lens,  and  the  vitreous  humor.  The- 
eyeball  is  contained  in  the  orbit,  in  v^hich  cavity  it  is  well 
protected  against  external  injury  ;  in  the  orbit  the  eyeball 
is  embedded,  for  further  protection,  in  a  mass  of  adipose 
tissue. 

The  capsule  of  Tenon,  or  tunica  vaginalis  oculi,  is  a  serous 
membrane  vs^hich,  in  the  form  of  a  thin  sac,  surrounds  the 
eyeball,  separating  it  from  the  mass  of  adipose  tissue  irt 
which  it  is  embedded  ;  this  serous  membrane  serves  to 
facilitate  the  motions  of  the  eyeball. 

The  eyeball  measures  about  one  inch  in  its  transverse 
and  nine-tenths  of  an  inch  in  its  antero-posterior  diameter. 

If  we  examine  the  eyeball  we  find  that  it  is  a  globe> 
formed  by  the  placing  together  of  portions  of  two  spheres^ 
of  different  sizes.  The  anterior  sixth  of  the  globe  is  a  por- 
tion of  a  smaller  sphere,  while  the  posterior  portion,  in- 
cluding the  remaining  five-sixths,  is  composed  of  a  segment- 
of  a  larger  sphere. 

The  eyeball  is  composed  of  several  tunics  and  of  refract- 
ing media. 


452     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

1 .  The  tunics  of  the  eye  are  : 

(a)  The  sclerotic  and  the  coruea. 

(6)  The  choroid,  iris,  and  ciliary  processes. 

(c)  The  retina. 

2.  The  refracting  media  are  : 

{a)  The  aqueous  humor. 

(6)  The  crystalline  lens  and  its  capsule. 

(c)  The  vitreous  humor. 

{a)  The  sclerotic  is  a  dense,  firm,  fibrous,  opaque  mem- 
brane which  forms  the  external  tunic  of  the  posterioi*  five- 
sixths  of  the  eyeball  and  serves  to  maintain  its  form.  It  is 
thick  behind,  and  thin  and  tapering  toward  its  anterior  bor- 
ders. The  outer  surface  of  the  sclerotic  is  smooth,  white, 
and  glistening,  and  j)artly  covered  by  the  conjunctiva  ;  to 
it  are  attached  the  recti  and  oblique  muscles  ;  its  inner 
surface  is  brown,  owing  to  pigmentation.  The  sclerotic  is 
pierced  posteriorly  and  a  little  internal  to  the  middle  line 
by  the  optic  nerve,  the  sheath  of  which  becomes  continu- 
ous with  the  sclerotic  at  the  point  where  the  optic  nerve 
enters  it ;  it  is  also  pierced  by  numerous  fine  openings 
which  serve  to  transmit  the  fibres  of  the  optic  nerve.  In 
front  the  sclerotic  becomes  continuous  with  the  cornea, 
the  border  of  which  is  overlapped  by  that  of  the  sclerotic. 

The  cornea  is  the  tunic  of  the  anterior  sixth  of  the  eye- 
ball ;  it  is  almost  circular  in  its  outline  and  has  a  convex 
anterior  surface.  The  degree  of  convexity  varies  at  differ- 
ent ages  ;  it  is  more  convex  in  youth  than  in  old  age  ;  the 
convexity  also  varies  in  different  individuals.  The  cornea 
is  very  dense,  of  an  even  thickness,  and  transparent.  Ex- 
amined under  the  microscope  it  will  be  found  that  the  cor- 
nea consists  of  four  layers,  which  may  be  described  as 
follows  : 

The  first  or  outer  layer  consists  of  several  layers  of  epi- 
thelial cells  ;  the  outer  ones  are  scaly,  flattened  cells,  the 
middle  many-sided,  and  the  deepest  columnar  cells. 

The  second  layer  constitutes  the  cornea  2)Toper ;  it  con- 


THE   SENSES   AXD    THE   SENSORY    ORGANS.  453 

sists  of  a  perfectly  transparent,  very  dense,  fibrous  mem- 
brane, which  is  composed  of  many  layers  of  connective- 
tissue  fibres  which  are  continuous  with  those  of  the 
sclerotic.  Between  the  layers  of  connective  tissue  is  a 
cement  holding  them  together.  In  it  are  seen  open  spaces 
— the  corneal  spaces — each  of  which  is  nearly  filled  with  a 
stellate  ceU,  the  corneal  capsule. 

The  third  layer  is  called  the  posterior  elastic  lamina  ;  it 
is  a  firm,  elastic,  and  exceedingly  thin,  transparent,  homo- 
geneous membrane  which  covers  the  cornea  behind.  At 
the  border  the  membrane  breaks  into  fibres  which  are  con- 
nected with  the  sclerotic  and  the  choroid  coat  ;  some  of 
them  are  continued  into  the  iris. 

The  fourth  layer  consists  of  a  single  layer  of  fiattened, 
polygonal,  transparent  cells.  This  layer  forms  the  anterior 
part  of  the  lining  of  the  anterior  chamber  of  the  eyeball. 
The  cornea  is  a  non  vascular  structure,  but  is  freely  sup- 
phed  with  nerve-fibres  from  the  ciliary  nerves. 

(6)  The  second  tunic  of  the  eyeball  is  formed  by  the 
choroid  coat  behind,  by  the  iris  in  front,  and  by  the  cili- 
ary processes  at  the  point  where  the  cornea  and  sclerotic 
join. 

The  choroid  coat  is  a  thin,  very  vascular  membrane 
which  invests  the  eyeball  beneath  the  sclerotic.  Pos- 
teriorly and  a  little  internal  to  the  central  point  it  is 
pierced  by  the  optic  nerve.  Anteriorly  it  extends  as  far 
as  the  cornea,  where  it  is  connected  with  the  iris  by  a 
number  of   folds  called  the  ciliary  processes. 

The  choroid  consists  of  a  network  of  veins  and  arterioles 
from  the  short  ciliary  arteries.  From  these,  in  the  deeper 
parts,  a  delicate  capillary  network  is  formed,  which  is  sup- 
ported by  a  fine  stroma  and  contains  in  its  meshes  star- 
shaped  pigment-cells.  On  the  inner  surface  of  the  choroid 
there  is  a  thin,  structureless  membrane  which  separates  it 
from  the  pigmentary  layer  of  the  retina. 

The  iris  is  a  thin,  circular  membrane  which  is  suspended 


454     LECTURES   ON    HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

in  the  aqueous  humor,  behind  the  cornea  and  in  front  of 
the  crystaUine  lens.  The  iris  is  contractile  and  presents, 
a,  little  internal  to  its  centre,  an  opening — the  jyupil.  By 
its  border  the  iris  is  connected  with  the  choroid;  exter- 
nal to  this  is  the  ciliary  muscle,  which  connects  the  iris 
"with  the  cornea  and  with  the  sclerotic.  The  anterior  sur- 
face of  the  iris  is  of  different  colors  in  different  individuals, 
hence  the  name  iris  Ca  rainbow).  The  posterior  surface  is 
■covered  by  a  dark  pigment  and  has  a  deep  purple  color. 
The  iris  consists  of  the  following  structures: 

1.  The  stroma.  This  is  composed  of  fine  bundles  of  fib- 
rous tissue  which  radiate  toward  the  periphery.  Some  of 
them  are  arranged  circularly  at  the  circumference.  These 
fibres  form  an  interlacing  network  containing  blood-vessels 
and  nerves  and  a  number  of  branching  cells.  The  latter 
•contain  pigment-granules  in  dark-eyed  individuals,  which 
are  absent  in  light-colored  or  blue  eyes. 

:2.  A  layer  of  many-sided  cells,  located  in  front. 

■3.  Involuntary  muscular  fibres.  These  consist  of  radiat- 
ing and  circular  fibres.  The  latter  constitute  the  sphincter 
of  the  pupil;  they  are  located  in  the  posterior  surface  of 
the  iris,  around  the  opening  of  the  pupil.  The  radiating 
fibres  constitute  the  dilator  of  the  pupil;  they  converge 
from  the  circumference  of  the  iris  to  the  margin  of  the 
pupil,  where  they  blend  with  the  circular  fibres. 

4.  Pigment.  This  is  found  in  the  form  of  gianules  in  the 
ifine,  polyhedral  cells  in  the  anterior  or  posterior  surface 
of  the  iris.  The  quantity  and  location  of  the  pigment  de- 
cide the  light  or  dark  color  of  the  eye. 

The  ciliary  muscle  is  a  ring  of  non-striated  muscular 
fibres,  consisting  of  circular  and  radiating  fibres,  which 
pass  from  the  iris  to  the  choroid.  This  muscle  serves  to 
accommodate  the  eye  for  the  vision  to  near  objects. 

The  iris  is  freely  supplied  with  blood-vessels  and  nerves. 
In  the  foetus  the  pupil  is  closed  by  a  delicate  vascular  mem- 


THE    SENSES    AND    THE    SENSORY    ORGANS.  455 

brane,  the  memhrana  ijciijillaris.  At  about  the  eighth 
month  of  intrauterine  life  this  begins  to  disappear. 

(c)  The  third  tunic  of  the  eyeball  is  formed  by  the  retina. 
The  retina  is  a  thin,  delicate  membrane  which  consists 
mainly  of  the  peripheral  expansion  of  the  optic  nerve,  with 
which  it  is  continuous  at  the  central  portion  behind  where 
the  optic  nerve  penetrates  the  sclerotic  and  choroid.  The 
outer  or  posterior  surface  of  the  retina  is  directed  toward 
the  inner  surface  of  the  choroid:  the  inner  surface  of  the 
retina  is  du-ected  toward  the  vitreous  humor.  In  the 
centre  of  the  internal  surface  of  the  retina  is  a  rounded 
elevation  which  is  called  the  yellow  spot  of  Sommering,  or 
the  macula  lutea:  this  has  a  central  depression,  the  fossa 
centralis. 

When  examined  under  a  microscope  it  will  be  found 
that  the  retina  is  an  exceedingly  complex  structure,  con- 
sisting of  ten  layers.  Beginning  at  the  outer  one,  these 
may  be  enumerated  as  follows: 

1.  The  pigrnentarii  layer.  This  is  the  external  layer, 
and  consists  of  a  single  layer  of  many-sided  epithehal  cells 
which  are  filled  with  pigment-granules. 

2.  Jacoh's  membrane  consists  of  a  layer  of  rods  and  cones, 
which  have  also  been  termed  the  neurO'epitlieliv.m.  The 
rods,  which  in  man  are  more  numerous,  are  arranged  with 
their  long  axes  perpendicular  to  the  surface,  and  consist 
of  an  outer  and  inner  portion.  The  former  presents  deh- 
cate  transverse  and  longitudinal  strise.  The  inner  portion 
is  granular  and  communicates  with  the  rod-granules  in 
the  outer  nuclear  layer. 

The  cones  are  flask-shaped  bodies,  which  are  directed 
with  their  tapering  end  toward  the  choroid,  and  with  the 
broad  end  toward  the  membrana  limitans  externa.  The 
cones,  hke  the  rods,  are  made  up  of  two  portions,  an 
outer  and  an  inner.  The  outer  presents  a  striation  similar 
to  that  of  the  outer  p  jrtion  of  the  rods:  the  inner  portion 


456     LECTURES   ON   HUMAN   PHYSIOLOGY    AND    HISTOLOGY. 

of  the  cones  is  granular,  expands,  and  is  connected  with 
the  cone-granules  of  the  outer  nuclear  layer. 

3.  The  membrana  limitans  externa  is  an  exceedingly 
delicate  membrane  separating  the  layer  of  cones  and  rods 
from  the  external  granular  layer. 

4.  The  external  granular  layer  consists  of  a  mass  of 
small,  round,  nucleated  and  bipolar  cells,  which  are  con- 
nected by  their  processes,  through  the  membrana  limitans 
externa,  with  the  rods  and  cones  of  Jacob's  membrane. 
Because  of  their  connection  with  these  elements  they  are 
called  rod-granules  and  cone- granules.  The  granular  cells 
are  supported  by  a  delicate  connective-tissue  stroma  :  this 
layer  is  also  called  the  outer  nuclear  layer. 

5.  The  outer  molecular  layer  consists  of  small,  granular 
cells  and  a  dense  network  of  fine  nerve-fibrillae. 

6.  The  internal  granular  layer  resembles  in  its  structure 
the  external  granular  layer.  It  consists,  like  this,  of  small, 
rounded,  nucleated,  granular  bipolar  cells  ;  this  structure 
is  also  called  the  inner  nuclear  layer. 

7.  The  inner  molecular  layer  resembles  in  structure  the 
outer  molecular  layer,  but  is  thicker. 

8.  The  vesicular  layer  consists  of  large  gangUon-cells 
which  have  one  process,  which  passes  into  the  fibrous 
layer  and  is  probably  continuous  in  this  with  a  nerve- 
fibre. 

9.  llhe  fibrous  layer  is  composed  of  fibres  from  the  optic 
nerve  ;  these  fibres  pass  through  the  various  layers  of  the 
retina  and  terminate  in  this  fibrous  layer. 

10.  The  membrana  limitans  interna  is  the  inner  layer  of 
the  retina,  and  is  in  contact  with  the  membrane  covering 
the  vitreous  humor.  It  is  composed  of  fine  connective-tis- 
sue network. 

The  various  layers  of  the  retina  are  held  together  and 
supported  by  a  fine  connective-tissue  framework.  Its 
fibres  pass  into  the  various  layers,  with  the  exception  of 
the  rod  and  cone  layer.     The  external  and  internal  mem- 


THE   SENSES   AND   THE   SENSORY   ORGANS.  -io? 

brana  limitans    are   also   formed  by  the   fibres    of    this 
stroma. 

The  blood-supply  to  the  retina  is  by  the  arteria  centralis, 
which  is  accompanied  by  a  venule.  It  pierces  the  optic 
nerve  at  its  centre,  and  divides  into  several  branches  which 
anastomose  and  radiate  between  the  retina  and  the  mem- 
brane covering  the  vitreous  humor.  After  a  short  course 
between  these  they  pass  into  the  layers  of  the  retina  and 
break  up  into  a  capillary  plexus.  The  retina  extends  for- 
ward as  far  as  the  ciliary  muscle,  and  terminates  there  in 
a  ragged  edge  termed  the  ora  serrata. 

The  function  of  the  retina,  the  structure  of  which  shows 
it  to  be  a  delicate  nervous  membrane,  is  to  receive  images 
of  external  objects. 

2.  The  refracting  media  of  the  eye  are  those  structures 
which  serve  to  refract  rays  of  light  and  collect  them  upon 
the  retina. 

(a)  The  Aqueous  Humor.— The  aqueous  humor  is  the 
fluid  which  fills  the  anterior  and  posterior  chambers  of  the 
eyeball ;  it  is  alkaline  in  reaction  and  composed  principally 
of  water  and  sodium  chloride. 

The  anterior  chamber  is  the  space  bounded  in  front  by 
the  cornea,  behind  by  the  anterior  surface  of  the  iris. 
The  posterior  chamber  is  the  space  between  the  cihary  pro- 
cesses and  the  periphery  of  the  iris.  The  anterior  surface 
of  the  crystalline  lens  is  in  close  contact  with  the  posterior 
surface  of  the  iris. 

(6)  Tlie  Crystalline  Lens.— The  crystalhne  lens  is  a  trans- 
parent body  situated  in  front  of  the  vitreous  body  and 
behind  the  pupil ;  it  is  double  convex,  being  more  convex 
on  its  posterior  than  on  its  anterior  surface.  It  measures 
about  one-third  of  an  inch  in  its  transverse  and  one- 
quarter  of  an  inch  in  its  antero-posterior  diameter.  The 
crystalline  lens  consists  of  a  number  of  concentric  laminae 
and  a  central  nucleus.  Each  lamina  consists  of  delicate, 
prismatic,  parallel  fibres.     The  lens  is  enclosed  in  a  trans- 


458     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

parent  and  highly  elastic  membrane  which  is  called  the 
capsule  of  the  lens.  The  lens  and  its  capsule  are  held  in 
position  by  a  thin,  transparent  membrane,  the  suspensory 
ligament. 

(c)  Tlie  Vitreous  Humor. — The  vitreous  body  is  a  jelly- 
like, transparent,  albuminous  substance  which  is  enclosed 
in  a  delicate,  transparent  membrane,  the  hyaloid.  The 
vitreous  body  is  contained  in  and  fills  the  concavity  of  the 
retina  ;  in  front  it  is  bounded  by  the  convex  posterior  sur- 
face of  the  crystalline  lens. 

The  structures  which  I  have  thus  described  are  those 
which  compose  the  eyeball.  Requisite  for  the  proper 
activity  and  use  of  the  eye  are  a  number  of  accessory 
structures — viz.,  the  conjunctiva,  the  lachrymal  appara- 
tus, the  eyelids,  the  eyelashes,  and  the  muscles  of  the  eye. 

The  conjunctiva  is  a  thin  membrane,  covered  with  epi- 
thelial cells,  which  covers  the  inner  surface  of  the  eyelids 
and  in  front  of  the  eyeballs.  The  conjunctiva,  being  mu- 
cous membrane,  serves  to  moisten  the  surface  of  the  eye- 
ball with  its  secretion. 

The  eyelids  are  two  thin  folds  which  are  placed  in  front 
of  the  eyeball;  they  are  movable  and  serve  to  protect  the 
eye  by  their  closure.  They  are  composed  of  integument, 
subcutaneous  areolar  tissue,  muscular  fibres,  thin  carti- 
laginous plates,  and  a  conjunctival  lining;  the  latter  con- 
tains numerous  Meibomian  glands,  the  secretion  of  which 
prevents  adhesion  of  the  eyelids  to  the  globe. 

The  eyelashes  are  rows  of  short,  thick  hairs  attached  to 
the  free  edges  of  the  eyelids;  they  serve  to  prevent  the 
access  of  foreign  particles  to  the  eye. 

The  lachrymal  apparatus — consisting  of  the  lachrymal 
glands,  the  lachrymal  sac,  and  the  nasal  duct — serves  to 
moisten  the  surface  of  the  eyeball  by  secretion. 

The  muscles  of  the  eyeball  are  the  external,  the  internal, 
and  the  superior  rectus  and  the  superior  and  inferior 
oblique  muscles.     These  muscles  are  voluntary,  and   by 


THE   SENSES   AND   THE   SENSORY   ORGANS.  459 

their  action  produce  such  movements  of  the  eyeball  as  are 
required  for  the  proper  viewing  of  an  object. 

The  optical  apparatus  of  the  eye  consists  of  the  follow- 
ing structures: 

1.  The  retina,  which  is  the  peripheral  terminal  expan- 
sion of  the  optic  nerve.  The  nervous  membrane  is  stimu- 
lated by  the  rays  of  light  falling  upon  it;  the  impulse  is 
transmitted  by  the  optic  nerve  to  the  brain,  causing  the 
sensation  of  vision. 

'2.  The  refracting  media,  which  serve  to  converge  and  to 
collect  upon  one  point  on  the  retina  the  rays  of  light  which 
pass  from  every  external  body  in  all  directions. 

3.  The  iris  is  a  contractile  structure  which  controls  the 
opening  of  the  pupil  for  the  purpose  of  regulating  the 
quantity  of  light  admitted  into  the  eye. 

4.  The  ciliary  muscle,  which  regulates  the  crystalline 
lens  so  that  objects  can  be  seen  at  various  distances. 

The  structure  of  the  retina  as  a  nervous  membrane  I 
have  already  described.  Its  special  function  is  to  receive 
Jight-impressions;  the  optic  nerve  itself  cannot  be  stimu- 
lated by  light. 

The  refracting  media  are  placed  in  front  of  the  retina 
for  the  purpose  of  collecting  the  rays  of  light  upon  one 
point  of  the  retina  and  thus  producing  a  distinct  vision. 
If  these  media  were  absent  the  rays  of  light  which  pass 
from  a  luminiferous  body  in  all  directions  would  strike  all 
points  of  the  retina  and  produce  the  sensation  of  light  in 
contradistinction  from  darkness,  but  would  not  produce  a 
distinct  vision. 

The  cornea,  owing  to  its  form  and  structure,  may  well 
be  considered  as  an  important  refracting  medium  of  the 
optical  apparatus.  First,  since  it  is  a  transparent,  solid 
substance,  all  rays  of  light  are  bent  from  their  original 
course  in  passing  through  it  from  a  rarer  medium;  second, 
iihe  outer  surface  of  the  cornea  is  convex,  and  all  rays  of 


460     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

light  falling  upon  a  convex  transparent  surface  are  con- 
verged as  they  pass  through  the  medium. 

The  use  of  the  aqueous  humor,  which  fills  the  anterior 
and  posterior  chamber,  is  probably  the  serving  as  a  me- 
dium for  the  movements  of  the  iris.  The  use  of  the  aque- 
ous humor  as  a  refracting  medium  is  not  fully  explained. 

The  most  important  refracting  medium  of  the  optical 
apparatus  is  the  crysfalUne  lens;  its  effectiveness  as  a  re- 
fracting medium  is  explained  by  its  form  and  structure.. 
The  uses  of  the  vitreous  body  are  principally  to  fill  the  eye- 
ball and  to  maintain  the  distance  of  the  lens  from  the  retina. 

The  manner  in  which  images  of  objects  are  thrown  upon 
the  retina  is  governed  by  the  physical  laws  of  the  refrac- 
tion of  rays  of  light.  As  you  are  familiar  with  these  law^s, 
and  also  with  the  shape  and  consistency  and  position  of 
the  various  refracting  media  of  the  optical  apparatus,  you 
do  not  require  a  detailed  description  of  this  subject.  I  will 
only  say  that  the  distinctness  of  the  image  formed  upon, 
the  retina  depends  upon  the  exact  focussing  upon  the  re- 
tina of  the  rays  emitted  from  a  luminiferous  body.  The 
optical  apparatus  of  the  eye  is  so  constructed  as  to  be  able 
to  bring  to  a  perfect  focus  upon  the  retina  the  rays  of  light 
emitted  from  objects  at  various  distances.  This  property 
is  described  as  the  accommodation  of  the  eye. 

The  focal  distance  is  the  distance  between  the  surface  of 
the  lens,  through  which  the  rays  have  been  transmitted, 
and  the/oc«.S' — viz.,  the  point  at  which  the  rays  are  col- 
lected. The  length  of  the  focal  distance  depends  upon  the 
convexity  of  the  lens  and  upon  the  distance  at  which  the 
object  is  placed  in  front  of  the  lens. 

The  focal  distance  increases  as  the  distance  of  the  object 
from  the  lens  decreases,  and  vice  versa.  The  focal  dis- 
tance increases  with  the  convexity  and  density  of  the  lens, 
and  vice  versa. 

The  optical  apparatus,  in  order  to  be  able  to  adapt  itself 
to  the  vision  of  objects  at  different  distances,  must  be  pro- 


THE   SENSES    AND    THE   SENSORY   ORGANS.  461 

vided  with  an  appliance  by  which  either  the  convexity  and 
density  of  the  crystalhne  lens  and  of  the  cornea  are  altered, 
or  by  which  the  distance  between  the  retina  and  the  lens 
■can  be  changed  ;  in  fact,  the  power  of  accommodation  of 
the  eye  has  received  various  explanations. 

HelmhoUz's  theory  as  to  the  cause  of  the  accommodation 
of  the  eye  is  now  almost  universally  adopted.  It  is  be- 
lieved that  the  adaptation  of  the  eye  for  objects  at  different 
distances  is  caused  by  a  change  in  the  convexity  of  the 
interior  surface  of  the  lens  ;  for  near  objects  it  becomes 
more  convex,  and  vice  versa. 

The  power  to  change  the  convexity  of  the  surface  of  the 
lens  is  not  an  inherent  property.  The  changes  are  caused 
by  the  action  of  the  ciliary  muscle  :  the  contraction  of  this 
increases  the  tension  of  the  suspensory  ligament,  and  so 
-somewhat  flattens  and  decreases  the  convexity  of  the  lens. 
Relaxation  of  the  ciliary  muscle  has  the  reverse  effect. 

The  focussing  of  rays  of  light  is  also  regulated  to  some 
-extent  by  the  central  opening  of  the  iris — viz.,  the  pupil. 
In  viewing  near  objects  the  pupil  contracts,  and  vice  versa. 
The  contraction  and  dilatation  of  the  pupil  under  vari- 
ous circumstances  may  be  enumerated  as  follows : 
1.  It  contracts — 

(a)  When  the  eye  is  exposed  to  bright  light. 
(6)  When  viewing  near  objects, 
(c)  When  the  eyes  converge  to  look  at  near  objects. 
{d)  After  local  administration  of  eserine. 
(e)  After  internal  administration  of  opium,  aconite, 
and  in  the  first  stages  of  alcohol  and  chloro- 
form poisoning. 
■2.  It  dilates — 

(a)  When  the  eye  is  exposed  to  dim  light. 
(6)  When  viewing  distant  objects, 
(c)  After  local  or  internal  administration   of  atro- 
pine or  similar  alkaloids. 


462     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

{d)  In  the  latter  stages  of  opium,  chloroform,  and 

alcohol  poisoning. 
(e)  In  paralysis  of  the  third  nerve. 

The  defects  of  the  optical  apparatus  may  exist  in  the 
refracting  media  or  in  the  accommodation  power.  The 
visual  disturbances  produced  by  these  defects  are  :  1.  Those 
produced  by  defects  in  the  refractive  media— viz.,  myopia, 
hypeimetropia,  and  astigmatism.  2.  The  defect  of  dis- 
turbance produced  by  loss  or  decrease  of  the  accommoda- 
tion power  is  known  sls  J) resbyopia— the  far-sightedness  of 
old  people. 

Myopia,  or  short-sightedness,  is  caused  by  the  fact  that 
the  eyeball  is  too  long  antero  posteriorly,  and  that  the  dis- 
tance from  the  lens  to  the  retina  is  too  great.  In  this 
condition  the  lens  is  probably  more  convex  ;  the  result  is 
that  objects  are  focussed  in  front  of  the  retina  ;  this  defect 
is  corrected  by  concave  glasses. 

Hypermetropia,  or  long-sight,  is  due  to  the  reverse  de- 
fects. In  this  condition  objects  are  focussed  behind  the 
retina  ;  the  defect  is  corrected  by  convex  glasses. 

Astigmatism  as  a  defect  is  due  to  a  greater  curvature  of 
the  eye  in  one  meridian  than  in  others  ;  the  result  is  that 
various  rays  are  not  equally  focussed.  The  condition  is 
obviated  by  cylindrical  glasses. 

The  normal,  or  emmotropjic,  eye  is  so  arranged  that 
parallel  rays  are  brought  to  a  focus  upon  the  retina  with- 
out any  effort  at  accommodation. 


QUESTIONS   AND   EXERCISES. 

Subject. — Tlie  Special  Senses. 
Lectures  XLVL  to  XLVIII.  inclusive. 

730.  Name  the  special  senses. 

731.  Distinguish  between  special  and  general  sensation. 

732.  Name  the  various  forms  of  peripheral  terminations 
of  the  sensory  nerves  of  the  skin  and  mucous  membrane. 


QUESTIONS   AND     EXERCISES.  463 

733.  Which  is  the  nerve  of  the  special  sense  of  taste  ? 

734.  Describe  the  papillae  of  the  tongue. 

735.  Which  is  the  nerve  of  the  special  sense  of  smell  ? 

736.  Which  is  the  nerve  of  the  special  sense  of  hearing  ? 

737.  Give  a  short  description  of  (a)  the  external,  (6)  the 
middle,  (c)  the  internal  ear. 

738.  Name  the  ossicles  of  the  ear. 

739.  What  is  the  Eustachian  tube  ? 

740.  Explain  how  the  sensation  of  hearing  is  produced. 
74:1.  Name  the  nerve  of  the  special  sense  of  sight. 

742.  Name  the  tunics  of  the  eye. 

743.  Name  the  refractive  media  of  the  eye. 

744.  What  is  the  retina  ? 

745.  What  is  the  conjunctiva  ? 

746.  Name  the  muscles  of  the  eyeball. 

747.  Name  the  essential  structures  of  the  optical  appara- 
tus of  the  eye. 

748.  What  do  you  understand  by  accommodation  ? 

749.  What  is  the  pupil  ? 

750.  What  causes    dilatation    and    contraction    of    the 
pupil  ? 

751.  How  is  the  sensation  of  sight  produced  ? 

752.  Explain  the  following  terms  :  emmetropia  ;   hyper- 
metropia  ;  myopia  ;  presbyopia  ;  astigmatism. 


LECTTJEE    XLTX. 

REPRODUCTION— GROWTH — DEVELOPMENT — THE  MALE  AND 
THE  FEMALE  SEXUAL  PRODUCTS  AND  ORGANS. 

The  functions  of  reproduction  have  for  tlieir  object  the 
preservation  of  the  species.  In  man  this  process  is  the 
result  of  the  union  of  the  male  and  female  sexual  products; 
this  takes  place  in  the  female  sexual  organs. 

The  union  is  preceded  by  a  development  of  the  sexual 
product.  Reproduction  is  a  process  of  growth  and  develop- 
ment. 

The  female  sexual  products  are  the  ovi;  the  male  sexual 
products,  the  spermatozoa.  The  human  ovum  is  a  typical 
cell;  it  is  spherical,  about  2T0  to  y^  of  an  inch  in  dia- 
meter, and  consists  of  a  cell-wall,  a  cell-contents,  a  nu- 
cleus, and  a  nucleolus. 

The  cell- wall  is  transparent  and  is  termed  the  zona 
pellucida  or  vitelline  membrane.  The  cell-body  filling  the 
limiting  membrane  is  called  the  yolk  or  vitellus. 

The  nucleus  is  termed  the  germinal  vesicle,  and  the  nu- 
cleolus contained  within  this  is  the  macula  germinaiiva,  or 
vitelline  spot,  or  germinal  spot. 

The  zona  pellucida  is,  as  I  have  stated  before,  a  trans- 
parent, colorless  membrane.  The  yolk  consists  of  a  granu- 
lar protoplasm  contained  in  the  meshes  of  a  delicate 
reticulum.  The  germinal  vesicle  is  contained  nearly  in 
the  centre  of  the  yolk,  and  consists  of  a  delicate,  trans- 
parent limiting  membrane  containing  a  clear  substance 
with  few  granules.  The  germinal  spot  is  contained  near 
that  portion  of  the  periphery  of  the  germinal  vesicle  which 
is  nearest  to  the  periphery  of  the  ovum. 


THE   FEMALE    SEXUAL   ORGAXS.  465 

The  ovi  are  developed  and  contained  in  the  ovaries. 
The  ovaries  are  two  oval-shaped  bodies,  situated,  one  on 
each  side  of  the  uterus,  in  the  broad  ligament  and  below 
the  Fallopian  tubes.  An  ovary  consists  of  a  serous  cover- 
ing, a  peculiar  soft,  vascular  stroma,  and  in  the  meshes 
of  this  a  number  of  smaU  vesicular  bodies  called  the  ovi- 
sacs or  Graafian  follicles.  The  serous  covering  of  the 
ovaries  is  covered  with  a  single  layer  of  columnar  epithehal 
cells  which  is  termed  the  germinal  epithelium. 

The  Graafian  follicles  are  round  and  of  various  sizes; 
they  consist  of  an  external  fibrous  vascular  coat,  and  an 
internal  coat,  which  is  fined  by  a  layer  of  cells,  termed  the 
membrana  granulosa.  The  vesicle  is  filled  with  a  trans- 
parent albuminous  fiuid  in  which  is  suspended  the  ovum. 

The  formation  of  the  Graafian  vesicles  and  of  the  ovi 
commences  before  birth;  their  development  and  matura- 
tion continue  from  puberty  until  the  menopause. 

The  ovi  are  formed  from  the  cells  of  the  germinal  epi- 
thelium ;  these  enlarge  and  become  involuted.  Small  depres- 
sions containing  these  cells  form  on  the  surface  of  the 
ovary  and  finaUy  become  encapsulated .  The  walls  of  the 
Graafian  vesicles  develop  from  processes  of  the  stroma. 
The  Graafian  follicles  are  small  before  puberty.  At  that 
period  the  ovaries  enlarge,  become  more  vascular,  and  the 
Graafian  follicles  enlarge  and  approach  the  surface  of  the 
ovary.  As  they  do  so  the  cells  of  the  membrana  granu- 
losa collect  into  a  mass  called  the  discus  proligerus;  in 
this  the  ovum  becomes  embedded.  As  the  Graafian  vesicles 
mature  and  approach  the  surface  of  the  ovary  they  burst, 
and  the  fluid  and  the  ovum  pass  into  the  Fallopian  tubes 
or  oviducts. 

The  Fallopian  tubes,  or  oviducts,  are  two  tubular  ducts, 
one  on  each  side,  situated  in  the  upper  border  of  the  broad 
figaments,  and  serve  to  conduct  the  ovi  to  the  uterus. 
Each  Fallopian  tube  consists  of  a  fimbriated  extremity,  a 
dilated  portion,  and  the  isthmus  or  constricted  portion. 

30 


466     LECTURES  ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

The  tube  consists  of  an  external  serous,  a  middle  mus- 
cular coat  consisting  of  longitudinal  and  circular  non- 
striated  fibres,  and  an  inner  mucous  coat  lined  with  colum- 
nar ciliated  cells. 

The  ufenis  is  the  organ  of  gestation,  and  is  contained, 
like  the  ovaries  and  Fallopian  tubes,  in  the  pelvic  cavity. 
It  is  the  organ  which  receives  the  fecundated  ovum,  sup- 
porting the  ovum  during  the  development  of  the  foetus. 
In  the  normal  condition  the  uterus  is  pear-shaped  and 
consists  of  a  body,  the  fundus,  and  of  a  neck  or  cervix. 
The  external  opening  of  the  cervix  opens  into  the  vagina. 
The  uterus  is  placed  between  the  bladder  in  front  and  the 
rectum  behind,  and  is  held  in  position  by  ligaments. 

The  cavity  is  triangular.  At  each  of  the  superior  angles 
is  the  opening  of  the  Fallopian  tube.  The  lower  angle  has 
the  opening  into  the  neck  of  the  uterus;  this  is  called  the 
ostium  uteri  internum. 

The  uterus  is  composed  of  an  external  serous,  a  middle 
muscular,  and  an  internal  mucous  coat. 

The  muscular  coat  forms  the  main  mass  of  the  organ, 
and  consists  of  non-striated  fibres  which  are  disposed  in  an 
external  longitudinal  and  an  internal  circular  layer. 

The  mucous  coat  consists  of  columnar  ciliated  cells  and 
presents  the  openings  of  numerous  tubular  glands,  the 
uterine  glands.  The  organ  is  freely  supplied  with  blood- 
vessels and  nerves. 

The  vagina  is  the  channel  which  extends  from  the  ute- 
rus to  the  vulva,  the  external  opening  of  the  genital  tract. 

In  the  human  female  maturation  and  expulsion  of  the 
ovum  occur  once  in  every  lunar  month.  During  the  de- 
velopment of  the  Graafian  vesicle  the  uterine  mucous  mem- 
brane undergoes  a  development  preparatory  for  the  recep- 
tion of  the  impregnated  ovum.  The  developed  mucous 
membrane  is  termed  the  nidus,  or  decidua  menstrualis.  If 
the  ovum  is  impregnated  this  membrane  serves  to  retain 
the  ovum  in  the  uterine  cavity,  and  later  on  constitutes 


THE   FEMALE   SEXUAL   ORGAXS.  467 

the  decidua  vera.  If  no  impregnation  has  taken  place  the 
decidua  menstrualis  undergoes  a  destructive  process  and 
is  ehminated,  a  process  which  is  accompanied  by  a  hemor- 
rhage from  the  surface  of  the  uterine  cavity,  which  consti- 
tutes the  menstrual  flow. 

Menstruation  is,  therefore,  the  result  of  the  destruction 
and  shedding  of  the  nidus  or  decidua  menstrualis.  The 
menstrual  flow  consists  of  blood,  shreds  of  the  decidua 
menstrualis,  epithehum,  and  mucus  ;  it  has  a  dark  color, 
a  pecuhar  odor,  and  does  not  readily  coagulate.  Menstrua- 
tion generally  occurs  once  every  lunar  month  :  the  inter- 
vals are,  however,  longer  or  shorter  in  different  individuals. 
The  flow  lasts  from  three  to  six  days,  and  is  often  preceded 
by  a  heavy  feeling  in  the  pelvis  and  by  pains  in  the  loins 
and  limbs. 

The  menstrual  period  generally  begins  at  the  age  of 
fourteen  or  fifteen  years.  The  time  of  the  first  appearance 
varies,  however,  in  different  climates,  and  is  also  influenced 
by  the  mode  of  hfe  and  the  habits  of  the  individual.  The 
first  appearance  of  the  menstruation  is  the  principal  sign 
of  the  commencement  of  puberty.  The  flow  recurs  at 
more  or  less  regular  intervals  during  the  whole  fruitful 
period  of  the  life  of  the  woman,  which  ends  generally  be- 
tween the  forty-fifth  and  fiftieth  year.  The  menstrual 
flow  is  generaUy  absent  during  pregnancy  and  during  the 
time  of  nursing  ;  cases  where  the  flow  occurs  during  these 
periods  are  not  rare. 

Observation  and  chuical  facts  tend  to  show  that  men- 
struation occurs  at  the  period  of  the  discharge  of  an  ovum, 
and  that  this  discharge  occurs  just  before  the  beginning  of 
the  menstrual  flow.  It  must,  therefore,  be  supposed  that 
conception  occurs  just  before  the  menstrual  flow,  not  im- 
mediately after  it  ;  the  fecundated  ovum  is  consequently 
that  which  is  discharged  prior  to  the  first  absent  men- 
struation. 

The  fact  that  extirpation  of  both  ovaries  causes  a  cessa- 


468      LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

tion  of  the  menstruation  tends  to  show  that  there  is  a  con- 
nection between  the  discharge  of  the  ovum  and  menstrua- 
tion, although  cases  are  not  rare  in  which  menstruation 
has  been  absent  for  several  months  and  still  conception 
took  place  ;  this  shows  that  menstruation  does  not  depend 
upon  the  discharge  of  the  ova. 

The  Graafian  vesicle,  after  its  rupture  and  after  the  dis- 
charge of  the  ovum,  undergoes  certain  changes  which 
result  in  the  formation  of  a  yellowish  body  called  the  coi^- 
pus  luteum.  This  is  a  rounded,  solid  mass  of  a  yellowish 
color,  and  consists  of  a  number  of  lobules  and  a  central 
cavity  which  is  filled  with  a  whitish,  trabeculated  mass. 

After  rupture  the  walls  of  the  Graafian  vesicle  become 
thickened  by  the  development  of  a  fleshy-looking  substance 
on  the  inner  layer  of  the  walls.  This  is  then  thrown  into 
folds  or  lobules  by  the  contraction  of  the  outer  layer,  leav- 
ing a  central,  stellate,  cicatricial  cavity.  The  yellowish 
color  of  the  corpus  luteum  is  produced  by  the  increase  of 
the  cells  of  the  membrana  granulosa  of  the  inner  wall  of 
the  Graafian  vesicle  ;  the  central  whitish,  stellate  mass  is 
fibrin  of  the  blood  resulting  from  the  rupture  of  the  vesicle. 

If  no  impregnation  of  the  ovum  takes  place,  only  a  small 
amount  of  yellow  mass  is  developed  ;  the  corpus  luteum 
assumes  the  size  of  about  three-quarters  of  an  inch,  then 
contracts,  and  finally  disappears  at  about  the  second  month. 

The  corpus  luteum  formed  under  these  circumstances  is 
termed  the  corpus  luteum  spurium.  If  impregnation  of  the 
ovum  does  take  place  the  yellow  substance  continues  to 
develop  throughout  the  whole  period  of  pregnancy,  result- 
ing in  the  production  of  the  large  corpus  luteum  of  preg- 
nancy, called  the  corpus  luteum  verum. 

The  Semen  of  the  Male. 

The  semen  of  the  male  is  the  fluid  secreted  by  the  testes, 
the  vesiculse  seminales,  the  prostate  gland,  and  Cowper's 


THE   MALE    SEXUAL    ORGANS.  469 

glands,  which  structures  must  be  considered  as  the  male 
sexual  organs. 

The  testes  consist  of  a  body,  the  epididymis,  and  the  vas 
deferens.  The  body  consists  of  the  seminal  tubules  ;  these 
are  convoluted  tubules  composed  of  a  basement  membrane 
lined  with  several  layers  of  secreting  epithelial  cells  called 
seminal  cells;  these  cells  are  disposed  in  two  layers — an 
outer  or  peripheral,  and  a  central  or  inner  layer.  The 
latter  are  the  active  cells  from  which  the  spermatozoa  are 
formed  ;  they  are  called  the  spermatoblasts.  The  seminal 
tubules  are  held  together  by  trabeculce.  The  whole  organ 
is  surrounded  by  a  tough,  fibrous  membrane  termed  the 
tunica  albuginea ;  external  to  this  is  a  serous  covering, 
the  tunica  vaginalis. 

The  epididymis  is  located  at  the  back  part  of  the  testi- 
cle ;  it  is  a  very  convoluted  tube,  which,  unwound,  is 
about  twenty  feet  long.  It  is  lined  with  ciliated  columnar 
epithelium,  and  constitutes  the  lower  portion  of  the  duct  of 
the  testicle. 

The  vas  deferens  is  the  duct  proper  of  the  testicle  ;  it  is 
about  two  feet  long,  and  begins  at  the  lower  and  back  part 
of  the  epididymis,  with  which  it  is  continuous  ;  it  is  com- 
posed of  a  fibrous  coat  and  a  mucous  lining  covered  with 
columnar  epithelium;  between  the  fibrous  and  the  mu- 
cous coats  is  a  layer  of  plain  muscular  fibres.  Its  diameter 
is  smaller  than  that  of  the  epididymis  ;  it  pursues  a  very 
tortuous  course  upward  along  the  posterior  part  of  the  tes- 
ticle and  inner  side  of  the  epididymis,  through  the  sperma- 
tic canal,  to  the  internal  abdominal  ring  ;  it  then  descends 
into  the  pelvic  cavity  to  the  side  of  the  bladder,  on  which 
it  passes  downward  to  the  base  and  to  the  urethra.  At  the 
base  of  the  prostate  gland  it  unites  with  the  duct  of  the 
vesicula  seminalis,  forming  one  common  duct,  the  ejacula- 
tory  duct,  which  opens  into  the  prostatic  portion  of  the 
urethra. 

The    vesiculce    seminales    are   two  convoluted  pouches 


470     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY, 

placed  at  the  base  of  the  bladder  external  to  the  vasa 
deferentia.  They  serve  as  reservoirs  for  the  seminal  fluid 
secreted  in  the  testes ;  they  also  secrete  a  fluid  which  is 
mixed  with  the  semen.  Their  ducts  unite  with  those  of 
the  vasa  deferentia. 

The  prostate  gland  is  placed  at  the  neck  of  the  bladder, 
surrounding  the  posterior  end  of  the  urethra.  The  organ 
is  composed  of  a  dense  fibrous  capsule  of  muscular  fibres 
and  of  glandular  tissue.  The  latter  consists  of  follicular 
expansions  which  communicate  with  channels  ;  these  join 
and  form  a  number  of  excretory  ducts  which  open  into  the 
prostatic  portion  of  the  urethra.  The  secreting  portion  of 
the  gland  is  lined  with  columnar  epithelium.  Cowper^s 
glands  are  two  small  glandular  bodies  situated  beneath  the 
mucous  membrane  of  the  membranous  portion  of  the  ure- 
thra ;  they  eliminate  their  secretion  by  two  long  ducts 
which  open  into  the  bulbous  portion  of  the  urethra. 

The  testes  are  freely  supplied  with  blood-vessels  and 
nerves  ;  these  and  the  ducts  of  the  testes  are  contained  in 
the  spermatic  cord. 

The  secretion  of  the  structures  just  described  constitutes 
the  semen ;  this  is  composed  of  the  liquor  seminis  and  of 
the  spermatozoa  and  of  detached  epithelial  cells. 

The  liquor  seminis  consists  of  an  albuminous  fluid. 

The  spermatozoa  are  microscopical,  elongated  organ- 
isms consisting  of  a  pointed,  elongated  head,  a  long,  fili- 
form, rounded  body,  and  a  long,  thin,  slender  tail.  In  the 
living  spermatozoa  this  tail  is  in  a  constant  wavy  lateral 
motion  ;  in  man  the  tail  is  longer  than  in  any  other  mam- 
malia. 

The  seminal  fluid  is  secreted  continuously  and  is  stored 
in  the  vesiculae  seminales  ;  from  these  it  is  discharged 
during  coition  or  spontaneously  into  the  bladder.  The 
secretion  of  semen  occurs  very  slowly,  except  under  special 
excitement. 

It  is  unknown  exactly  what  ingredient  makes  the  semen 


THE   MALE   SEXUAL,   ORGANS.  471 

capable  of  impregDating  the  female  ovum,  but  the  fact 
that  the  spermatozoa  exist  in  the  impregnating  fluid  of 
all  animals  tends  to  show  that  they  are  essential  for  the 
act  of  impregnation. 


LECTURE    L. 

THE   FECUNDATION   OF    THE   OVUM,    AND   THE    IMMEDIATE 

CHANGES   TAKING   PLACE   IN   THE   OVUM   AFTER   ITS 

IMPREGNATI  ON 

The  fecundation  of  the  ovum  is  caused  by  the  entrance 
of  a  single  spermatozoon  into  it.  This  takes  place  either  in 
the  ovary  (which  explains  the  occurrence  of  abdominal 
pregnancies),  or,  as  is  generally  the  case,  in  the  Fallopian 
tube.  The  spermatozoon  passes  to  the  tube  by  its  own  mo- 
tion. 

The  ovum  passes,  in  from  two  to  three  weeks,  through 
the  Fallopian  tube,  and  once  in  the  uterine  cavity  it  is  not 
again  subject  to  impregnation. 

The  spermatozoa  enter  the  Fallopian  tube,  and  the  one 
which  first  approaches  the  escaped  ovule  enters  it  with  its 
head,  while  its  filiform  tail  becomes  detached  and  disap- 
pears. I  have  stated  before  that  as  the  ovule  matures  its 
germinal  vesicle  approaches  the  surface  of  the  ovule  and 
undergoes  certain  changes,  which  always  take  place  and 
are  independent  of  the  fecundation  of  the  ovule.  These 
changes  areas  follows:  At  about  the  time  of  maturation  of 
the  ovule  a  portion  of  the  germinal  vesicle  is  detached  and 
pushed  outward  beneath  the  vitelline  membrane;  this  con- 
stitutes the  first  polar  (jlohule.  Then  a  second  portion  of  the 
germinal  vesicle  is  similarly  detached  and  pushed  outward; 
this  is  called  the  second  jyolar  globule.  The  remaining  por- 
tion of  the  germinal  vesicle  passes  back  toward  the  centre 
of  the  vitellus  and  becomes  a  round,  nuclear  body  called 
the  female  protonucleus.  At  the  time  of  these  changes 
there  takes  place  a  shrinking  of  the  vitellus. 


THE   DEVELOPMENT   OF   THE   FCETUS.  473 

The  head  of  the  spermatozoon  which  enters  the  ovule 
passes  toward  the  female  protonucleus,  becomes  a  rounded 
body,  and  constitutes  the  male  protonucleus.  This  gradu- 
ally approaches  the  female  protonucleus  and  finally  fuses 
with  it  into  one  mass.  This  constitutes  the  process  of  fe- 
cundation. 

The  first  change  after  fecundation  is  that  the  germinal 
spot,  or  female  protonucleus — that  is,  the  nucleus  formed 
by  the  fusion  of  the  male  with  the  female  protonucleus — 
divides  into  two  nuclei.  This  is  followed  by  a  division  of 
the  vitellus,  so  that  as  the  result  of  this  division  two  cells  of 
an  unequal  size  are  formed;  these  are  called  the  vitelline 
spheres.  The  smaller  of  the  two  is,  for  the  sake  of  dis- 
tinction, called  the  hyj^oblastic  cell;  the  larger,  or  upper, 
the  epiblastic  cell.  These  then  continue  to  divide  and  sub- 
divide, until  as  the  result  of  this  continued  cleavage  a  mul- 
berry-shaped mass  is  formed,  which  is  called  the  blastoderm. 
The  division  of  the  cell  takes  place  by  indirect  division, 
mitosis  or  karyokinesis — a  process  which  I  have  described 
^n  detail  in  a  former  lecture;  the  viteUine  membrane 
takes  no  part  in  this  division.  This  constitutes  an  invest- 
ment of  the  impregnated  ovum;  another  transparent  albu- 
minous investment  forms  around  the  ovule  as  it  passes 
through  the  Fallopian  tube. 

As  the  blastoderm  develops,  its  outermost  cells — viz.,  those 
derived  from  the  epiblastic  cell  or  sphere — show  a  ten- 
dency to  divide  at  a  much  more  rapid  rate  than  the  cells  of 
the  inner  layer — viz.,  those  derived  from  the  hypoblaatic 
cell  or  sphere. 

The  epiblastic  cells  gradually  form  a  layer  around  the 
hypoblastic  cells,  so  that  after  a  while  we  find  the  blasto- 
derm to  consist  of  a  central  or  inner  layer  of  cells  from  the 
hypoblast  and  of  an  outer  layer  of  cells  from  the  epiblast. 

.  Owing  to  the  slower  rate  of  division,  the  hypoblastic  cells 
are  larger  but  fewer  in  number  than  those  of  the  outer  or 
epiblastic  layer.     The  cells  of  the  inner  or  hypoblastio  layer 


474     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

at  this  time  become  more  granular.  Gradually  a  fluid  col- 
lects between  these  two  layers  of  cells,  separating  them, 
except  at  the  ends  where  they  remain  united. 

The  mass  of  cells  within  the  vitelline  membrane,  consist- 
ing of  the  two  layers  just  described,  is  called  the  blasto- 
dermic membrane;  it  consists  at  this  period  of  two  layers — 
viz.,  the  outer  or  ejnblastic,  and  the  inner  or  hypoblastic 
layer;  they  are  also  called  the  ectoderm  and  the  endoderm. 
Gradually  a  third  layer  develops  between  the  two — the 
mesoblastic  layer  or  mesoderm.  It  is  believed  that  this  is 
formed  from  cells  of  the  epiblast  and  hypoblast;  however, 
nothing  definite  is  known  about  it. 

The  blastodermic  membrane  consists  eventually  of  three 
layers — viz.,  the  hypoblast  or  endoderm,  the  epiblast  or 
ectoderm,  and  the  mesoblast  or  mesoderm. 

From  these  layers  the  various  structures  of  the  embryo 
are  developed  as  follows: 

1.  From  the  hypoblast,  endoderm,  or  inner  layer:  (a)  The 
internal  epithelium — viz.,  that  of  the  alimentary  canal,  of 
the  respiratory  tract,  and  that  of  the  glands  opening  into 
these.     (6)  The  allantois. 

2.  From  the  epiblast,  ectoderm,  or  outer  layer:  (a)  The 
epidermis  and  all  its  involutions.  (6)  The  nerve  structures 
— viz.,  the  brain,  spinal  cord,  the  nerves,  etc. 

3.  From  the  mesoblast,  mesoderm,  or  middle  layer:  All 
the  other  embryonal  structures — viz.,  the  vascular  organs, 
the  organs  of  locomotion,  the  connective  tissues,  the  geni- 
to-urinary  organs,  etc. 

The  position  in  w^hich  the  embryo  is  about  to  develop  in 
the  ovum  is  first  seen  in  the  blastoderm  as  a  central 
rounded,  opaque  spot  resulting  from  a  congregation  of 
cells  at  this  place.  This  is  termed  the  area  germinativa, 
the  first  form  of  which  is  that  of  a  round  disc;  gradually 
it  becomes  elongated  and  constricted  at  the  centre,  assum- 
ing a  lady-finger  shape.  The  central  portion  of  this  area 
becomes   transparent  and  is  called   the     area  pellucida. 


THE   DEVELOPMENT   OF   THE   FCETUS.  475 

The  next  change  is  the  appearance  of  a  shallow  groove, 
visible  as  a  finer  streak  in  the  posterior  part  of  the  area 
pellucida.  This  is  terraed  the  primitive  trace  or  the 
primitive  groove.  Simultaneously  with  these  changes  the 
already-described  separation  of  the  cells  of  the  blastoderm 
into  two  layers — viz.,  the  epiblast  and  the  hypoblast — 
takes  place,  and,  after  the  appearance  of  the  primitive 
trace,  the  middle  layer  or  mesoblast  is  formed.  After 
these  changes  the  development  of  the  foetal  structures, 
known  as  the  medullary  groove,  the  laminae  dorsales,  the 
notochord,  and  the  protovertebrse,  takes  place. 

The  medidlary  groove  is  formed  by  the  folding  of  cells 
of  the  epiblast.  It  begins  in  the  anterior  part  of  the  area 
germinativa,  and  gradually  extends  over  the  whole  length 
of  the  primitive  tract.  This  folding  of  the  cells  results  in 
the  formation  of  a  groove,  the  sides  and  bottom  of  which 
are  formed  by  cells  from  the  epiblast. 

The  space  between  the  epiblast  and  the  hypoblast  is 
filled  with  the  cells  of  the  mesoblast.  The  epiblastic  cells 
which  form  the  sides  of  the  groove  develop  into  two  late- 
ral plates,  called  the  lamincB  dorsales  or  medidlary  plates. 
These  finally  come  together  at  their  free  ends,  thus  form- 
ing a  closed  canal,  called  the  neural  or  medidlary  canal, 
which  is  formed  and  lined  by  cells  of  the  epiblastic  layer 
alone. 

The  cells  lining  the  neural  canal  develop  into  nerve- 
centres;  those  covering  the  canal  develop  into  epidermis 
of  the  head  and  back.  The  cephalic  extremity  of  the  neu- 
ral canal  gradually  dilates,  and  from  it  develops  the  brain, 
while  from  the  remaining  constricted  portion  the  spinal 
cord  develops. 

At  the  bottom  of  the  neural  canal  the  cells  of  the  epi- 
blastic layer  come  together  with  those  of  the  hypoblastic 
layer,  so  that  the  cells  of  the  mesoblast  between  them  be- 
come separated  into  two  thick  masses,  which  are  arranged 
at  the  sides  of  the  neural  canal.     The  next  change  is  that 


476     LECTURES   ON  HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

a  mass  of  the  cells  from  the  hypoblast  becomes  thickened 
and  finally  detached  from  its  layer.  This  is  termed  the 
notocJiord.  This  is  located  at  the  bottom  of  the  neural 
canal  and  between  the  epiblastic  and  the  hypoblastic  layers. 
These  two  layers  at  this  period  are  no  longer  in  contact, 
but  separated  from  each  other.  The  thickened  masses 
from  the  mesoblastic  layer  which  are  located  at  the  sides 
of  the  neural  canal  gradually  become  separated  from  the 
remainder  of  the  mesoblastic  layer,  which  is  situated  late- 
rally to  the  protovertebra,  and  thus  divides  into  two  layers. 
One,  which  covers  the  hypoblast,  is  called  the  splanchno- 
pleura;  the  other,  which  covers  the  epiblast,  is  called  the 
somatopleura.  From  the  former  the  muscular  and  other 
mesoblastic  structures  of  the  viscera  are  developed;  from  the 
latter  the  cutis  vera  and  the  skeletal  muscles.  The  space 
between  these  two  layers  forms  the  pleuro-peritoneal  cav- 
ity. The  embryo,  which  has  so  far  developed  from  the 
cells  of  that  part  of  the  blastodermic  membrane  which  is 
known  as  the  area  germinativa,  is  at  this  period  merely  a 
straight  structure.  It  now  becomes  more  and  more  curved 
at  its  cephalic  and  caudal  extremities,  so  that  fiDally  the 
blastodermic  membrane  becomes  constricted  at  the  point 
of  the  curvature  of  the  extremities  of  the  embryo.  The 
blastodermic  membrane  thus  assumes  an  hour-glass  shape, 
the  smaller  globe  or  portion  of  which  is  formed  by  that  part 
of  the  blastodermic  membrane  from  which  the  embryo  so  far 
lias  developed,  while  the  larger  portion  or  globe  is  developed 
by  the  remainder  of  the  blastodermic  membrane.  This 
larger  portion  is  termed  the  ijolk-sac  or  the  umbilical 
vesicle,  the  interior  of  which  communicates,  at  the  point 
of  constriction  of  the  blastodermic  membrane,  with  the 
interior  of  the  smaller  globe.  This  point  of  constriction 
is  the  place  of  the  ;future  umbihcus.  The  constriction 
gradually  increases,  so  that  the  cavity  of  the  yolk  is  divided 
into  halves — one  which  constitutes  the  interior  of  the 
umbilical  vesicle,  and  one  which  develops  into  the  intestinal 


THE    DEVELOPMENT    OF    THE    FOETUS.  477 

cavity  of  the  embryo.     At  the  point  of  constriction  there 
remains  an  opening,  the  omphalo-mesenieric  duct. 

The  umbihcal  vesicle,  at  this  period  of  the  embryonic 
development,  serves  to  supply  nutrition  for  the  embryo. 
The  walls  of  the  umbilical  vesicle  are  formed  by  the  epi- 
blast  and  the  hypoblast,  with  the  inner  layer  of  the  divided 
mesoblast — viz.,  the  splanchnopleura — between  the  two. 

The  function  of  the  umbilical  vesicle  as  an  organ  for  the 
nutrition  of  the  embryo  ceases  at  about  the  sixth  week. 
During  this  period  two  vessels,  called  the  omplialo -mesen- 
teric vessels,  develop,  which  absorb  the  fluid  contents  of 
the  vesicle.  This  dries  up  and  becomes  small,  but  remains 
visible  until  the  fourth  or  fifth  month  of  pregnancy.  At 
about  the  sixth  week  a  new  foetal  structure  is  developed, 
called  the  aUcmtois,  and  serves  for  the  vascular  connection 
between  the  embryo  and  the  maternal  uterine  vessels. 
The  allantois  is  a  part  of  the  chorion;  this  is  one  of  the 
three  membranes  which  invest  the  embryo  during  its  de- 
velopment. 

These  three  foetal  membranes  are  :  the  amnion,  the  cho- 
rion, and  the  decidua. 

The  amnion  is  the  first  of  the  foetal  membranes  which  is 
developed.  It  is  formed  from  embryonal  structures,  and  is 
the  membrane  which  immediately  surrounds  the  foetus 
during  the  whole  period  of  gestation. 

The  process  of  the  formation  of  the  amnion  is  as  follows  : 
At  the  point  of  constriction  of  the  blastodermic  membrane 
(viz.,  at  the  caudal  and  cephahc  ends  of  the  embryo)  a 
fold  of  the  somatopleura  (viz.,  of  the  epiblast)  and  the 
parietal  layer  of  the  divided  mesoblast  becomes  inflected 
and  arches  backward  over  the  sides  and  back  of  the  em- 
bryo, until  finally  the  two  folds  meet  and  fuse  over  the 
dorsum  of  the  embryo,  which  thus  becomes  totally  in- 
vested by  a  bag  which  is  composed  of  two  layers — viz.,  an 
inner  from  the  epiblast,  and  an  outer  from  the  parietal 
layer  of  the  mesoblast  at  the  point  of  fusion  of  the  two 


478     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

folds.  The  epiblastic  layer  of  the  amnion  becomes  re- 
flected and  lines  the  inner  surface  of  the  vitelline  mem- 
brane constituting  the  chorion.  That  part  of  the  amnion 
which  directly  covers  the  embryo  is  called  the  true  amnion, 
while  the  reflected  layer  of  the  amnion  is  termed  the  false 
amnion.  The  space  between  the  two  is  filled  with  a  thick- 
ish  fluid  and  communicates  with  the  pleuro-peritoneal 
cavity — viz.,  with  the  space  between  the  parietal  and  the 
visceral  layers  of  the  divided  mesoblast. 

The  space  between  the  true  amnion  and  the  embryo  is 
called  the  amniotic  cavity.  It  gradually  becomes  filled 
and  expanded  with  a  fluid  called  the  liquor  amnii.  This  is 
composed  of  water,  salts,  small  amounts  of  albumin,  and 
urea.  This  fluid  steadily  increases  until  about  the  fifth  or 
sixth  month  of  gestation.  It  serves  to  protect  the  embryo 
from  external  violence,  and  to  afford  an  equal  support  for 
the  development  of  the  foetus. 

The  chorion  is  the  second  of  the  foetal  membranes.  It  is 
also  developed  from  foetal  structures,  and  is  composed  of 
the  following  parts  :  1,  the  vitelline  membrane  ;  2,  the  re- 
flected portion  of  the  amnion — viz.,  the  false  amnion  ;  and 
3,  the  allantois,  a  structure  which  develops  between  the 
two  layers  of  the  mesoblast. 

As  the  chorion  develops,  fringe-like  processes  arise  from 
the  external  surface.  These  are  at  first  fibrous  and  cover 
the  whole  external  surface;  later  on  they  become  vascu- 
lar and  form  villi,  and  develop  only  on  that  part  of  the  ex- 
ternal surface  which  is  to  form  the  foetal  portion  of  the 
placenta. 

The  allantois  is  a  structure  which  develops  from  the 
hypoblast  and  visceral  layer  of  the  mesoblast — viz.,  the 
splanchnopleura  ;  it  arises  from  the  caudal  end  of  the  body 
cavity  of  the  foetus  as  a  hollow  vesicle.  This  gradually 
expands  between  the  walls  of  the  pleuro-peritoneal  cavity, 
and  finally  spreads  over  and  unites  with  the  internal  sur- 
face of  the  false  amnion — viz.,   the  inner  layer   of  the 


THE    DEVELOPMENT    OF    THE    FCETUS.  479 

chorion.  Blood-vessels,  termed  the  allantoic  vessels,  develop 
in  the  allantois,  and  from  there  minor  branches  pass  into 
the  fringe-like  processes  of  the  external  surface  of  the 
chorion,  which  thereby  become  villi.  The  allantoic  vessels 
are  the  channels  through  which  the  embryo  receives  its 
nutrition.  They  finally  constitute  the  vessels  of  the  um- 
bilical cord. 

The  decidua  is  developed  from  the  mucous  membrane  of 
the  uterus.  In  my  last  lecture  I  stated  that  before  the 
ovum  reaches  the  uterine  cavity  the  mucous  membrane  de- 
velops for  reception  and  retention  of  the  ovum  in  case  it  is 
fecundated,  and  that,  if  such  is  not  the  case,  the  developed 
uterine  mucous  membrane  is  shed  with  the  menstrual  flow. 
When  the  impregnated  ovum  reaches  the  uterine  cavity  it 
becomes  completely  embedded  in  folds  of  the  raucous  mem- 
brane. That  portion  of  the  membrane  which  surrounds  the 
ovum  is  termed  the  decidua  reflexa,  while  the  portion  upon 
which  the  ovum  rests  is  termed  the  decidua  vera.  This 
covers  the  uterine  walls  ;  it  becomes  very  vascular,  and  its 
vessels  communicate  directly  with  the  sinuses  of  the  ute- 
rus. That  portion  of  the  decidua  vera  which  develops  into 
the  placenta  is  called  the  decidua  serotina.  When  the  im- 
pregnated ovum  reaches  the  uterine  cavity  the  opening  of 
its  neck  becomes  closed  by  a  plug  of  mucus.  Gradually 
the  decidua  serotina  and  the  villi  of  the  chorion  which  are 
in  contact  with  it  develop  and  form  the  placenta,  the  or. 
gan  by  which  the  connection  between  the  mother  and  the 
foetus  is  maintained  throughout  the  remainder  of  the  ute- 
rine gestation.  The  circulation  of  the  blood  between  the 
mother  and  the  foetus  takes  place  through  the  umbilical 
vessels — viz.,  two  arteries  and  one  vein,  the  former  con- 
veying venous  blood  from  the  foetus  to  the  placenta,  the 
latter  arterial  blood  from  the  placenta  to  the  foetus.  These 
vessels  are  derived  from  the  allantoic  vessels.  The  umbili- 
cal cord,  consisting  of  the  coils  of  the  umbilical  vessels 
surrounded  by  a  gelatinous  tissue,  is  therefore  developed 


480     LECTURES   ON   HUMAN  PHYSIOLOGY   AND    HISTOLOGY. 

from  the  allantois;  it  appears  at  about  the  end  of  the  fifth 
week.  The  omphalo-mesenteric  vessels  and  the  umbihcal 
duct  have  become  obhterated  by  this  time. 


LECTURE   LL. 

THE   DEVELOPMENT   OF   THE   FCETUS. 

In  speaking  of  the  further  development  of  the  foetus  I 
will  briefly  describe  the  development  of  the  principal  parts 
— viz.,  of  the  spine,  the  ribs,  sternum,  limbs,  cranium  and 
face,  the  vasculatory  system,  the  respiratory,  digestive,  and 
genito-urinary  apparatus,  and  the  nerve  and  muscle  tissues. 
In  giving  the  periods  of  the  development  of  these  various 
parts,  I  will  follow  the  chronological  table  of  Beaune 
and  Banchard. 

During  the  first  week  the  impregnated  ovum  is  in  the 
Fallopian  tube  and  undergoes  but  little  change  in  size  and 
form.  During  the  second  week  the  ovum  passes  into  the 
uterine  cavity ;  it  becomes  embedded  there  in  the  decidua  and 
rapidly  increases  in  size.  The  amnion,  the  allantois,  the 
medullary  groove,  the  uotochord,  the  neural  canal,  and  the 
separated  masses  of  mesoblast  at  either  side  of  the  neural 
canal,  are  developed  during  the  second  week,  so  that  at  the 
end  of  the  week  there  is  a  distinct  indication  of  the  devel- 
oping embryo. 

The  spinal  column  now  begins  to  form  in  the  following 
manner:  The  mesoblastic  masses  on  each  side  of  the  neu- 
ral canal  begin  to  segmentate  laterally,  until  at  each  side 
we  find  a  series  of  quadrilateral  masses  which  in  number 
correspond  to  the  number  of  the  permanent  vertebrje. 
These  segments  extend  forward  and  inward  until  they  sur- 
round the  notochord,  which  is  situated  in  front  of  the  neu- 
ral canal,  occupying  the  place  of  the  bodies  of  the  forming- 
vertebrae.  Gradually  the  segments  extend  backward  and 
inward,  surrounding  the  neural  canal.     The  notochord  and 

31 


482     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

the  neural  canal  are  thus  enclosed  by  a  mass  of  mesoblast 
which  constitutes  the  membranous  matrix  of  the  vertebrae. 
At  about  the  fifth  or  sixth  week  chondrification  of  these 
segments  begins. 

The  permanent  vertebra?  are  developed  from  the  adjoin- 
ing halves  of  two  of  the  above-described  protovertebral 
summits — the  part  which  extends  forward  surrounding  the 
notochord  forms  the  bodies,  the  part  enclosing  the  neural 
canals  forms  the  arches,  of  the  vertebrae.  The  canal  formed 
by  the  arches  of  the  so-formed  vertebrae  is  lined  with  epi- 
blast,  from  which  the  nerve  structures  of  the  spinal  cord  are 
developed;  the  spinal  column  is  surrounded  by  hypoblast. 

The  ribs  are  formed  by  lateral  extensions  from  the  verte- 
brae; these  extensions  pass  forward  and  inward,  become  de- 
tached from  the  vertebrae,  and  soon  become  cartilaginous, 
forming  membrano-cartilaginous  bars  corresponding  to  the 
number  of  the  ribs. 

The  sternum  is  formed  by  a  fusion  of  the  anterior  ends 
of  the  upper  nine  ribs  on  each  side. 

The  formation  of  the  cranium  begins  at  a  very  early 
period  by  a  bulbous  expansion  of  the  cephalic  end  of  the 
neural  canal. 

From  the  epiblastic  lining  of  this  part  of  the  neural  canal 
the  brain  is  developed,  while  from  the  epiblastic  layer  cover- 
ing this  part  of  the  neural  canal  the  scalp  is  formed.  The 
membranes  of  the  brain,  the  bones  of  the  cranium,  the  skin 
proper,  the  blood-vessels,  and  the  muscles  of  the  cranium 
are  developed  from  a  mesoblastic  mass  from  the  protover- 
tebral which  extends  upward  between  the  two  layers  of  the 
epiblast.  The  bulbous  expansion  of  the  cephalic  end  of  the 
neural  canal  gradually  divides  by  constriction  into  three 
compartments,  which  are  known  as  the  primary  cerebral 
vesicles.  The  epiblastic  lining  of  these  develops  ijito  brain 
structures  as  follows:  The  Uning  of  the  upper  vesicle  forms 
the  optic  thalamus,  the  cerebral  hemisphere,  and  the  corpus 
striatum  on  each  side;  that  of  the  middle  vesicle  forms  the 


THE    DEVELOPMENT   OF    THE    FCETUS.  483 

corpora  quadrigemina,  and  that  of  the  posterior  vesicle 
forms  the  medulla  oblongata;  the  communicating  interior 
of  the  three  vesicles  constitutes  later  on  the  general  ventri- 
cular cavity. 

The  vesicles  are  at  first  straight,  one  upon  another,  but 
are  gradually  bent  forward,  forming  a  double  curvature, 
the  anterior  or  lower  of  which  forms  the  frontal,  the  pos- 
terior or  upper  the  occipital,  protuberance.  I  have  already 
stated  that  a  mass  of  mesoblast  from  the  protovertebrse  ex- 
tends upward  between  the  two  epiblastic  layers,  and  that 
from  this  mesoblastic  mass  the  bones,  etc.,  of  the  cranium 
are  developed.  The  bones  of  the  base  of  the  cranium  are 
developed  by  a  chondrification  of  this  mass  which  takes 
place  at  about  the  fifth  or  sixth  week.  The  bones  of  the 
roof  of  the  cranium  are  developed  later  on  between  mem- 
branes. The  notochord  terminates  in  a  tapering  end  at  the 
cephalic  end  of  the  neural  canal,  and  is  embedded  in  the 
mesoblastic  mass  between  the  two  epiblastic  layers. 

The /ace  is  developed  in  a  similar  manner  as  the  spine 
and  the  cranium — viz.,  by  laminae  or  processes  which  be- 
come cartilaginous  and  develop  into  the  bones  of  the  face. 
These  processes  or  visceral  laminae  present  clefts  between 
them,  so  that  at  each  side  of  the  region  of  the  neck  and 
face  we  distinguish  four  such  clefts  and  arches.  The  first 
of  these  is  called  the  mandihular  arch;  it  contains  a  car- 
tilaginous mass,  at  the  distal  end  of  which  is  developed 
the  lower  jaw.  From  this  arch  a  process  extends  forward, 
from  which  the  superior  maxillary  and  the  malar  bones 
are  developed.  The  cleft  between  the  first  visceral  arch 
and  the  above-named  process  forms  the  mouth.  Some- 
times the  process  from  which  the  superior  maxillary  bone 
is  developed  does  not  fully  unite  in  the  middle  line;  the 
result  is  the  condition  which  is  familiar  to  all  of  you — viz., 
the  cleft  palate. 

From  the  other  visceral  arches  the  hyoid  and  portion  of 
the  temporal  bone  and  the  ossicles  of  the  ear  are  developed. 


484     LECTURES   ON    HUMAN   PHYSIOLOCiV   AND   HISTOLOGY. 

The  various  structures  of  the  hard  and  soft  parts  of  the 
face  are  the  result  of  this  differentiation  during  develop- 
ment. 

The  points  and  periods  of  ossification  of  the  jaws  and 
other  bones  of  the  face  you  will  learn  in  your  lectures  on 
anatomy. 

The  development  of  the  teeth  I  have  akeady  described 
in  detail  in  a  previous  lecture.  The  germs  of  the  teeth 
appear  first  during  the  sixth  iveek.  Ossification  of  the 
low^er  jaw  also  begins  during  that  week.  The  ossification 
of  the  upper  jaw  begins  during  the  seventh  week.  The- 
hard  palate  begins  to  unite  at  about  the  eighth  iveek. 

The  limbs  appear  about  the  fourth  week  as  leaf -like 
appendages  from  the  trunk.  By  about  the  eighth  week 
the  arms,  forearms,  thighs,  legs,  and  digital  clefts  are  dis- 
tinctly visible. 

The  development  of  the  blood  circulatory  system  goes 
through  three  distinctly  different  stages  before  the  regular 
system  is  complete.  We  have,  first,  the  vitelline  circula- 
tion, by  which  the  embryo  receives  its  nourishment  from 
the  3^olk  or  vitellus;  second,  the  placentcd  or  f(£tcd  circu- 
lation, where  the  foetus  derives  arterial  blood  from  the 
mother  through  the  placenta;  and,  third,  w^here  the  indi- 
vidual receives  its  nutrition  through  its  own  organs,  as  is 
the  case  after  birth. 

The  vitelline  circulation  consists  of  the  circulation  of  a 
fluid  between  the  area  vasculosa  of  the  yolk  and  the  em- 
bryo. 

The  circulatory  system  at  this  period  consists  of  a  heart 
which  is  nearly  tubular,  and  of  two  arteries  and  two  veins. 

The  fluid  circulating  in  this  system  is  blood  containing 
primitive  red  blood-corpuscles.  The  heart  is  developed  by 
the  formation  of  a  cavity  in  a  mass  of  cells  from  the  vis- 
ceral layer  of  the  mesoblast.  The  mass  of  cells  arranges 
itself  in  two  layers  around  this  excavation.  The  inner 
layer  forms  the  pericardium,  the  outer  tlie  muscle   sub- 


THE    DEVELOPMENT    OF    THE    FCETUS.  485 

stance  of  the  heart.  The  excavation  is  at  first  separated 
longitudinally  in  the  centre,  so  that  in  the  earliest  stages 
of  development  the  heart  consists  of  two  tubes  placed 
side  by  side.  Each  of  these  has  an  artery  and  a  vein. 
Later  on  the  two  tubes  coalesce,  so  that  the  heart  consists 
of  one  tubule  with  two  arteries  and  two  veins. 

The  primitive  blood-vessels  at  this  stage  are  also  de- 
veloped from  mesoblastic  cells  of  the  visceral  layer. 

The  red  blood-corpuscles  at  this  period  are  formed  from 
the  nuclei  of  the  mesoblastic  cells.  These  nuclei  collect 
a  mass  of  protoplasm  around  themselves,  so  that  at  this 
early  period  they  resemble  white  blood-corpuscles.  Later 
on  they  assume  a  reddish  tinge  and  the  nucleus  disap- 
peai's. 

The  ivhite  blood-corpuscles  in  the  embryo  are  first  formed 
in  the  liver. 

As  the  umbilical  vesicle  diminishes  and  the  placenta  de- 
velops, important  changes  take  place  in  the  circulatory 
system. 

The  heart,  at  first  tubular,  becomes  elongated,  twisted 
upon  itself,  and  finally  divides  by  transverse  septa  into 
three  compartments.  The  posterior  of  these  forms  the 
auricles;  the  middle,  the  ventricles;  the  anterior,  the  aortic 
bulb,  at  which  the  large  vessels  at  the  root  of  the  heart 
are  developed. 

The  next  change  is  the  division  of  the  auricular  and 
ventricular  cavity  into  the  right  and  left  auricles  and 
ventricles. 

The  anatomy  and  characteristics  of  the  foetal  heart  and 
circulatory  apparatus,  as  well  as  the  placental  or  foE-tal 
circulation,  I  have  described  in  detail  in  a  previous  lecture, 
I  will,  therefore,  say  only  a  few  words  on  the  development 
of  the  blood  vessels.  In  speaking  of  the  vitelline  circula- 
tion I  said  that  it  was  maintained  by  a  tubular  heart,  two 
arteries,  and  two  veins.  As  the  placental  circulation  de- 
velops, the  two  arteries,  which  from  the  tubular  heart  pass 


486     LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

downward  along  the  primitive  spinal  column,  unite,  form- 
ing one  vessel,  the  aorta;  the  portion  of  the  two  primitive 
arteries  above  the  point  of  fusion  forms  the  primitive 
aortic  arches  from  which  the  vessels  of  the  head,  etc., 
a.rise. 

The  vessels  at  the  lower  part  of  the  body  are  developed 
at  the  same  time.  From  the  lower  end  of  the  aorta  two 
vessels  spring,  the  hypogastric  or  umbilical  arteries,  by 
which  blood  is  returned  to  the  maternal  placenta.  Later 
on  the  external  iliac  and  the  femoral  arteries  are  developed 
from  a  branch  which  arises  from  the  umbilical  arteries. 

In  speaking  of  the  development  of  the  veins,  we  must 
consider  them  under  two  headings^ — viz.,  visceral  and  pari- 
etal veins. 

The  visceral  veins  are  derived  from  the  vitelline  veins — 
viz.,  the  veins  which  return  the  blood  during  the  vitelline 
circulation. 

The  two  veins  later  on  unite,  forming  the  sinus  venosuSy 
which  opens  into  the  auricular  part  of  the  primitive  heart. 

The  two  vitelline  veins  enter  the  abdomen  and  pass  to 
ward  the  location  of  the  future  liver.  This  organ  now 
begins  to  form  around  the  vein  ;  branches  and  capillary 
plexuses  are  formed  from  them,  which  finally  form  the 
hepatic  veins,  the  portal  vein,  and  those  of  the  stomach 
and  intestines.  The  parietal  yqims  are  developed  from  two 
short  vessels,  called  the  cardinal  and  primitive  jugular 
veins,  which  return  the  blood  from  the  embryo  into  the 
auricular  portion  of  the  tubular  heart ;  these,  by  union, 
gradually  form  the  vena  cava,  the  iliac  veins,  etc. 

The  veins  from  the  lower  part  of  the  bod}^  are  developed 
from  the  cardinal,  those  of  the  head  and  upper  part  of  the 
body  from  the  primitive  jugular  veins. 

The  periods  of  the  development  of  these  various  parts 
are  as  follows  : 

The  first  indication  of  the  development  of  the  heart  is 
noticeable  at  the  end  of  the  second  week. 


THE    DEVELOPMENT    OF    THE    FOETUS.  487 

During  the  fourth  week  the  separation  of  the  heart  into 
a  right  and  left  half  is  complete.  The  activity  of  the  um- 
bilical vesicle  ceases  at  the  end  of  the  fifth  week,  when  the 
placental  circulation  is  established. 

The  development  of  the  alimentcu^y  canal  begins  at  a 
very  early  period  by  an  inflexion  of  hypoblast  ;  this  forms 
a  tube  which  extends  from  one  end  of  the  embryo  to  the 
other,  being  closed  at  the  caudal  and  cephalic  extremities  ; 
this  tube  freely  communicates  with  the  umbilical  vesicle. 
Gradually  the  tube  divides  into  three  compartments,, 
named  respectively  the  hind-gut,  mid-gut,  and  fore-gut. 
From  these,  then,  the  various  parts  of  the  alimentary  canal 
are  developed,  as  follows  :  from  the  fore-gut,  the  pharynx,, 
oesophagus,  stomach,  and  duodenum  ;  from  the  hind-gut^ 
the  rectum;  and  from  the  mid-gut,  the  remaining  portions. 

The  mouth  and  buccal  cavity  are  formed  by  involutions 
of  the  outer  layers  of  the  blastodermic  membrane  near  the 
upper  end  of  the  fore-gut. 

The  anus  is  similarly  formed  by  an  involution  at  the 
lower  end  of  the  hind-gut. 

The  liver  is  developed  at  about  the  end  of  the  third  week. 

The  gall-bladder  and  the  pancreas  are  developed  about 
the  second  month  ;  also  the  salivary  glands. 

The  7^esj)iratory  organs  begin  to  develop  at  about  the 
fourth  week  as  a  dilatation  or  diverticulum  from  the  mid- 
dle of  the  upper  part  of  the  fore-gut.  Gradually  a  pouch 
is  developed  at  either  side  of  this  diverticulum  ;  these  com- 
municate with  it,  and  through  it  with  the  upper  part  of  the 
fore-gut.  In  the  further  development  secondary  pouches 
are  formed  which  communicate  with  those  first  formed, 
and  thus  by  the  eighth  week  these  pouches  have  developed 
into  lobulated  lungs. 

The  portion  where  the  median  diverticulum  communi- 
cates with  the  upper  part  of  the  fore-gut  develops  into  the 
trachea  by  the  formation  of  cartilaginous  rings  ;  these 
form  during  the  seventh  week.     About  the  fourth  month 


488      LECTURES   ON   HUMAN   PHYSIOLOGY   AND   HISTOLOGY. 

the  larynx,  with  the  cartilages  and  vocal  cords,  is  formed. 
At  about  this  time  a  deUcate  membrane  develops  which 
separates  the  pleuro-peritoneal  cavity  into  two — viz.,  the 
thoracic  and  abdominal. 

The  skin  is  developed  from  the  external  and  middle 
blastodermic  membrane,  the  epidermis  from  the  external, 
the  true  skin  from  the  middle  layer.  A  distinction  of  the 
two  layers  of  the  skin  is  first  noticeable  at  about  the  fifth 
week. 

The  subcutaneous  and  adipose  tissues  are  only  developed 
at  the  fourth  month. 

The  nails  and  hair  appear  between  the  third  and  fifth 
months,  the  papilla?  about  the  sixth,  and  the  glands  of  the 
skin  about  the  same  period. 

The  development  of  the  eye  is  first  noticeable  by  the  ap- 
pearance of  the  primitive  ocular  vesicle,  which  is  formed 
during  the  third  week.  The  nervous  and  non-vascular 
structures  of  the  eye  are  developed  from  epiblasts;  the  vas- 
cular structures,  from  the  mesoblast.  The  process  of  the 
development  of  the  eye  is  too  complicated  to  be  described 
in  detail  in  the  short  time  I  can  spend  on  the  subject  of 
embryology. 

The  eyelids  are  formed  at  the  end  of  the  third  month; 
they  are  united  at  first,  but  separate  before  birth. 

The  development  of  the  ear  is  indicated  by  the  appear- 
ance of  the  primitive  aural  vesicle  at  the  end  of  the  third 
week,  shortly  after  the  appearance  of  the  primitive  ocular 
vesicle. 

Your  special  lecturer  on  the  eye  and  ear  will  dwell  in  a 
more  detailed  manner  on  the  further  development  of  these 
organs. 

There  remains  yet  for  me  to  say  a  few  words  on  the 
development  of  the  urinary  and  the  generative  organs- and 
the  nerve  structures. 

The  development  of  the  urinary  organs  is  rather  compli- 
cated; they  are  of  mesoblastic  origin. 


THE   DEVELOPMENT   OF   THE   FCETUS.  489 

The  kidneys  are  developed  from  the  lower  part  of  the 
set  of  tubular  glands  which  are  known  as  Wolffian  bodies. 
These  glands  consist  of  three  sets  of  tubular  organs;  each 
of  these  opens  with  one  end  into  the  body  cavity  of  the 
embryo,  with  the  other  end  into  the  hind- gut.  They  are 
situated  in  front  of  the  primitive  vertebral  column,  and 
each  has  an  excretory  duct. 

The  Wolffian  bodies  are  developed  by  the  end  of  the  third 
week;  they  increase  until  the  sixth  week,  then  gradually 
decrease,  and  disappear  about  the  third  month. 

The  kidneys  are  developed  from  the  posterior  or  lower 
set  of  these  tubular  glands,  or  segmental  organs,  as  they 
are  called;  their  excretory  ducts  are  the  ureters. 

The  urinary  bladder  is  formed  about  the  third  month  by 
a,  dilatation  of  the  lower  part  of  the  allantois. 

The  generative  organs  are  the  same  in  the  two  sexes  in 
the  first  stages  of  development.  The  first  indication  is  the 
appearance  of  the  genital  ridge,  which  is  a  thickening  of 
the  peritoneal  cavity  near  the  Wolfiian  body.  From  this 
ridge  are  developed  the  testicles  in  the  male  and  the  ovaries 
in  the  female.  A  distinction  of  the  sexes  is  perceptible  at 
about  the  seventh  week. 

The  external  genital  orgaris,  like  the  internal  organs,  pass 
through  a  stage  in  their  development  in  which  no  distinc- 
tion of  the  sexes  is  possible. 

The  first  step  is  that  the  cloacal  opening  is  separated  by 
a  septum  which  constitutes  the  future  perineum;  this  is 
formed  about  the  second  month.  The  posterior  part  of  the 
so-divided  cloacal  opening  constitutes  the  rectum;  the  an- 
terior part,  the  urogenital  sinus.  About  the  sixth  week  a 
small  elevation,  called  the  genital  tubule,  is  formed  in  the 
front  part  of  the  cloaca.  Gradually  this  tubercle  is  enclosed 
by  two  folds,  the  genital  folds.  Toward  the  second  month 
there  is  a  longitudinal  furrowing  of  the  genital  tubercle 
which  forms  the  genital  furrow. 

After  the   second   month    the    differentiation   of   these 


490     LECTURES   ON   HUMAN   PHYSIOLOGY   AND    HISTOLOGY. 

organs  takes  place.  In  the  female  sex  the  urogenital  sinus 
forms  the  vagina,  the  genital  tubercle,  the  clitoris,  and  the 
genital  folds  the  labia  of  the  vulva. 

In  the  male  sex  the  genital  tubercle  develops  into  the 
penis,  the  genital  furrow  into  the  urethra,  and  the  uro- 
genital sinus  forms  the  posterior  parts  of  the  urethra. 
These  parts  develop  during  the  third  and  fourth  months. 

The  nerves,  like  the  other  nerve  structures — viz.,  the 
brain  and  spinal  cord — are  developed  from  epiblast.  The 
primary  divisions  of  the  brain,  as  described  before,  are  vis- 
ible during  the  third  week. 

The  special  ganglia  and  the  roots  of  the  spinal  nerves  are 
perceptible  at  the  end  of  the  fourth  week.  The  posterior 
roots  of  the  spinal  nerves,  the  sheaths  of  the  nerves,  and 
membranes  of  the  nerve  centres,  are  formed  during  the 
sixth  week. 

The  nerve  structures  of  the  eye,  ear,  olfactory  apparatus 
are  developed  during  the  first  five  weeks.  The  finer  divi- 
sions of  the  great  nerve-centres  develop  during  the  third 
month.  The  first  indication  of  the  development  of  the 
sympathetic  nervous  system  is  visible  at  the  end  of  the 
eighth  week;  the  sympathetic  nerves  are  developed  from 
the  ganglia  of  the  spinal  nerves. 

This  completes  the  intrauterine  development  of  the  foetuSj 
as  briefly  as  possible,  but  the  new-born  infant  is  by  nO' 
means  successfully  developed.  In  my  last  lectures  I  have 
pointed  out  some  of  the  further  changes  which  the  indi- 
vidual undergoes  during  childhood  and  youth  and  puberty. 

The  development  of  the  body  is  complete  only  when 
adult  life  is  reached. 

Of  particular  interest  to  you  is  the  development  of  the 
teeth  and  jaws,  with  the  phases  of  which  you  are  all 
familiar. 

I  now  close  my  series  of  lectures  with  the  hope  that 
this  little  work  may  be  a  guide  in  your  studies  and  enable 
you  to  follow  the  subject  with  a  better  understanding. 


QUESTIONS   AXD   EXERCISES.  491 

QUESTIONS   AND   EXERCISES. 

Subject. — Reproduction,  Growth,  and  Development. 
Lectures  XLIX.-LI.  inclusive. 

753.  Describe  the  human  ovuni. 

754.  Explain  the  phenomena  of  menstruation. 

755.  What  is  a  Graafian  follicle  ? 

756.  Describe  a  spermatozoon. 

757.  Where  and  how  is  the  impregnation  of  the  ovum 
in  the  human  female  effected  ? 

758.  What  is  a  corpus  luteum  ? 

759.  What  is  the  first  change  in  the  ovule  after  its  im- 
pregnation ? 

760.  Name  the  layers  of  the  blastodermic  membrane. 
and  state  which  structures  are  developed  from  each. 

761.  At  what  period  are  the  germs  of  the  teeth  first 
visible  i 

762.  What  is  the  placenta  ? 

763.  Name  the  foetal  membranes. 

764.  Describe  in  brief  the  development  of  the  principal 
parts,  such  as  the  spinal  cord,  the  cranium,  the  face,  the 
respiratory  and  digestive  apparatus,  and  the  circulatory 
system. 


inde: 


A 

Abducent  nerve,  411 
Absorption,  the,  166 
Adenoid  tissue,  18 
Adipose  tissue,  18 
Air,  the  atmospheric,  22S 

respiratory  changes  of,  229 
Air-passages,  the,  219 
Alimentary  canal,  parts  of  the,  97 

canal,  development  of  the,  487 
Albumins,  the,  71 
Albuminoids,  the,  71 
Allantois,  the,  478 
Amoeba,  the,  3 
Amoeboid  motion.  3 
Amnion,  the,  477 
Anaemia,  48 
Anatomy,  visceral,    definition   of 

the  word,  1 
Animal  heat,  the,  292 

motion,  the,  301 
Antitoxin,  55 

Anus,  development  of  the,  487 
Arteries,  the,  191 
Assimilation,  the,  245 
Astigmatism,  462 
Auditory  nerves,  the,  413 
Auricle  of  the  ear,  the,  445 
Axis-cylinder,  the,  27 

B 

Bacteria,  73 

Basal  ganglia,  the,  of  the  brain, 
351 


Bile,  the,  146 
Bile-pigments,  the,  148 
Bile-salts,  the,  147 

Pettenkofer's  test  for,  147 
Bile,  action  and  uses  of  the,  152 
Biology,  1 
Bioplasma,  the,  2 
Blastema,  2 
Blastoderm,  10 

Blastodermic  membrane,  the  lay- 
ers of  the,  474 
Blood,  physiology  of  the,  32 

quantity  of,  47 

coagulation  of,  48 

gases  of,  45 
Blood-circulatory   system,    devel- 
opment of  the,  484 
Blood-corpuscles,  the,  34 

development  of  the  red,  485 

development  of  the  white,  485 
Blood-pressure,  the,  200 
Bone,  structure  of,  20 
Bi'ain,  stricture  of  the,  334 

fatigue  and  rest  of  the,  399 
Bronchi,  the,  221 
Buccal  cavity,  description  of  the, 
98 

development  of  the,  487 

C 

Canal,  Haversian,  in  bone  tissue, 

20 
Canaliculi,  in  bone  tissue,  20 
in  dentine.  22 


494 


INDEX. 


Capillaries,  the.  191 

Carbohydrates     in     the     human 
body,  63 
absorption  of  the,  178 

Carbonates  in  the  human  body,  62 

Cardiac  muscle,  the,  25 

Cartilage,  varieties  and  structure 
of,  19 

Cell,  the.  2 

Cell-body,  structure  of  the,  4 
changes  dui'ing  division.  9 

Cell-nucleus,  structure  of,  5 

Cell-division,  indirect.  7 

■Cells,  differentiation  of  the.  Id 
general  functions  of  the,  3 
special  functions  of  the.  11 
various  forms  of  the,  10 

Cemeutum,  22 

Centrasoma,  9 

Cerebellum,  anatomy  and    struc- 
ture of  the,  378 
the  medulla  of  the,  381 
peduncles  of  the,  382 
central  gray  mass  of  the,  383 
functions  of  the,  383 

Cerebi'um,  the,  335 

surfaces  of  the,  336 
fissures  of  the,  337 
sulci  of  the,  339 
lobes  of  the,  338 
convolutions  of  the,  34 
the  base  of  the,  347 
the  interior  of  the,  350 
general  ventricular  cavity  of 

the,  353 
the     fifth    ventricle    of    the, 

356 
the  third  ventricle  of  the,  358 
the  gray  matter  of  the  cortex 

of  the,  359 
the  gray  matter  of  the  basal 
ganglia  of  the.  361 


Cerebrum,  the  gray  matter  lining 
the  genei'al  ventricular  cav- 
ity of  the,  362 

the  white  nerve  substance  of 
the,  363 

fujictions  of  the,  367 

functions  of  the  cortex  of  the, 
368 

functions  of  the  basal  ganglia 
of  the,  375 
Chemotaxis,  43 
Chemotropismus,  43 
Chondrin,  19,  72 
Chorion,  the,  478 
Chromatolysis,  10 
Chromosoms,  8 
Chyle,  the,  171 

Chromatic  material  of  a  cell,  5 
Circulation,  the  renal.  261 

normal,  of  the  blood,  183 

foetal,  the,  213 

vitelline,  the,  484 
Coagulation  of  blood,  50 
Colloids,  definition  of.  174 
Coloring    matters,     the,    of    the 

body,  74 
Connective  tissues,  the,  17 
Corpuscles  of  blood,  the  red,  34 

the  white,  41 
Corpus  luteum,  the,  468 
Cord,  umbilical,  the,  479 
Cranial  nerves,  the,  401 
Cranium,  development  of  the,  482 
Crusta  petrosa,  22 
Cuticula.  22 

D 

Decidua  meustrualis,  466 

vera,  479 

reflexa,  479 

serotina,  479 
Defaecation,  157 


INDEX. 


495 


Deglutition,  the  act  of,  116 

stages  of,  119 

nerve  centre  of,  121 
Decomposition   products,    tiie,   in 

the  body,  74 
Deatin,  21,  101 
Dentinal  canals,  22 

sheaths,  22 

fibres,  22 
Development  of  the  embryo,  472 
Dextrin,  64 
Diabetes  mellitus,  65 
Diaster,  formation  of,  8 
Disc  of  Bowman,  25 
Discus  proligerus,  the,  465 
Diffusion  of  liquids,  173 
Digestion,  tlje,  97 
Digestive  juices,  the,  97 
Dispii'em,  formation  of,  8 
Dreaming,  400 

E 

Ear,  the  external,  445 

the  middle,  446 

the  internal,  448 

development  of  the,  474 
Ectoderm,  the,  10 
Eggs,  coinposition  of,  89 
Elastin,  72 
Emmotropia,  462 
Enamel,  101 
Endoderm,  10 
Endocardium,  184 
Endomysiam,  25 
Endoneurium,  28 
Endosmosis,  173 
Endosmotic  equivalent,  175 
Enzymes,  the,  72 
Epiblast,  10 
Epididymis,  the  469 
Epineurium,  28 
Epithelium,  simple,  13 

stratified,  14 


Epithelium,  transitional,  14 

glandular,  15 
Erythrocytes,  34 
Erythroblasts,  40 
Excretions,  the,  255 
Extremities,  the  development  of 

the.  484 
Eye,  development  of  the,  488 
structure  of  the,  451 

F 
Eacial  nerve,  the,  411 
Face,  development  of  the,  483 
Faeces,  composition  of  the,  157 
Fallopian  tubes,  the,  465 
Fats,  absorption  of  the,  178 
Fecundation,   the,   of   the   ovum, 

472 
Fehling's  solution,  66 
Fermentation  test,  the,  for  sugar, 

66 
Ferments,  the,  72 
Fibrinogen,  51 
Fibrinoplastin,  51 
Filtration,  the  process  of,  176 
Foetal  development,  the,  481 
Foetal  circulation,  the,  213 
Food,  the,  82 
Food-articles,  the  inorganic,  83 

the  organic,  85 

the  animal,  86 
Foramen,  apical,  the,  101 
Foi-ces,  the,  of  the  animal  organ- 
ism, 292 
Fourth  ventricle,  the,  of  the  brain, 

397 
Fruits,  the,  as  food  articles,  86 

the  leguminous,  85 

the  cereal,  85 
G 
Gall-bladder,  the,  150 

development  of  the,  487 


49G 


INDEX. 


Gases,  the,  of  the  blood,  45 

the,  in  the  body,  62 
Gastric  juice,  the,  126 
Gastrulation,  the,  10 
Generative  organs,  the  male,  469 

the  female,  464 
Genital  organs,    development  of 

the,  489 
Germinal  matter,  the,  2 
Germinal  spot,  the,  464 
Glands,  the  secreting,  15 

the,  of  the  stomach,  123 
Glucose,  65 
Glycogen,  65 
Globulins,  the,  71 
Glosso-pharyngeal     nerve,     the, 

14 
Graafian  follicles,  the,  465 
Granules,     elementary,     in      the 

blood,  44 

H 

Haematin,  36 

Hsematoidin,  38 

Hcemoglobin,  36,  72 

Hair,  the,  287 

Hearing,  the  sense  of,  445 

Heart,  the.  183 

action  of  the,  194 
nerve  supply  of  the,  196 
motor  ganglia  of  the,  198 
development  of  the,  485 

Heart-sounds,  the,  199 

Histologx',  definition  of.  1 

Humor,  the  aqueous,  of  the  eye, 
457 
the  vitreous,  of  the  eye,  458 

Hydrocarbonates,  the,  67 

Hypermetropia,  462 

Hypnotism,  400 

Hypoblast,  10 

Hypoglossal,  nerves,  the,  417 


Icterus.  149 

Ingredients,   the,    of  the   human 

l)ody,  60 
Inosit,  67 
Insalivation,  107 
Interglobular  spaces,  22 
Intestinal    digestion,    resume    of 

the.  154 
Iris,  the,  459 

E 

Karyokinesis,  7 
Karyolysis,  10 
Keratin,  72 

Kidneys,  anatomy  and  structure 
of  the,  256 
innervation  of  the,  273 
Kymograph,  the,  200 


Lacteals,  the,  168 

Lactose,  67 

Laevulose,  67 

Lamella  of  bone  tissue,  20 

Larynx,  the,  219 

Lens,  tlie  crystalline,  of  the  eye,. 

457 
Lesions,  valvular,  the   more  fre- 
quent, 211 
Leucocj'tes,  103 
Leukaemia,  48 
Linin,  5 

Liquor  sanguinis,  44 
Liver,    glycogenetic    function    of 
the,  248 

development  of  the,  487 
Lung-tissue,  structure  of  the,  223 
Lungs,  the.  221 

breathing    capacity    of    the, 
226 


INDEX. 


497 


Lymph,  the,  171 
Lymph-plasma,  171 
Lymph-corpuscles,  171 
Lymphatic   glands,    structure   of 

the,  169 
Lymphoid  tissue,  18 

M 

Macula  gf^rminativa,  the,  464 
Marrow  of  hone,  2  L 
Mastication,  the  act  of,  98 

muscles  of,  99 
Medulla   ohlongata,    anatomy    of 
the.  3S6 
oblongata,    structure   of  the, 

390 
oblongata,  the  gray  substance 

of  the,  392 
oblongata,    functions  of  the, 

393^ 
oblongata,  automatic  centres 

in  the,  394 
oblongata,    reflex   centres  in 
the,  396 
Medullary  canal,  475 

groove,  475 
Membrane,  the  blastodermic,  10 
the  blastodermic,   the  layers 

of,  10 
periodontal,  101 
Xasmeth's,  101 
Krause's,  25 
Membranes,  the  foetal,  477 
Menstruation,  the,  467 
Mesoblast,  10 
Mesoderm,  10 
Metals,  the,  in  the  human  body, 

62 
Metha?moglobin,  37 
Microsoms,  4 

Micturition,    mechanism   of    the, 
275 

32 


Milk,  the,  as  a  food  article,  88 
Mitosis,  7 

Monaster,  formation  of  the,  8 
Morphology,     definition     of    the 

word,  1 
Motion,  ciliary,  3 
Brownian,  3 
Motor  oculi  nerves,  the,  404 
Mucin,  72 
Muscles,  the,  of  the  eyeball,  459 

the  ciliary,  of  the  eye,  459 
Muscular  tissues,  the,  24 
Myopia,  462 

N 
Nails,  the,  288 
Nerve-tissue.  26 

Nerve-centres,   functions   of  the, 
320 
properties  of  the,  321 
Nerve-flbres,  functions  and   pro- 
perties of,  326 
Nerve  irritability,  328 
Nerve  substance,  composition  of, 
330 
substance,  nutrition  and  meta- 
bolism of,  332 
Nerves,  the  structure  of  the,  325 
electrical,  currents  in,  330 
development  of  the,  490 
Nervous  system,  the  physiology 

of  the.  318 
Neuroglia,  28 
Neurilemma,  28 
Nodes  of  Eanvier,  28 
Notochoi'd,  the.  476 
Nucleoplasm,  5 
Nucleus,  structure  of  the,  5 
Nucleoli,  structure  of  the,  5 

O 

Odontoblasts,  22,  100 
Odontoclasts,  105 


498 


INDEX. 


CEsophagus,  tlie,  119 
Olfactory  nerves,  the,  402 
Omphalo-mesenteric  duct,  the,  477 

vessels,  the,  477 
Optic  nerves,  the,  403 
Optical  apparatus,  the,  of  the  eye, 

459 
Organic    nitrogenized     proximate 

principles,  69 
Ossicles,  the,  of  the  ear,  446 
Osteoblasts,  31 
Ovaries,  the,  465 
Ovum,  the,  464 


Palate,  the,  117 
Pancreas,  the,  139 

development  of  the,  487 
Paralmin,  5 
Paraglobulin,  51 
Paranuclein,  6 
Pathetic  nerves,  the,  405 
Peptones,  71 
Pericardium,  184 
Pericementum,  23,  101 
Perimysium,  25 
Perineurium,  28 
Periosteum,  21 
Pliagocytosis,  43 
Pharynx,  the,  118 
Physiology,  definition  of,  1 
Plasma,  the,  of  blood,  44 
Plethora,  48 

Pneumogastric  nerves,  the,  414 
Polysemia,  48 

Pons  Varolii,  anatomy  and  sti'uc- 
ture  of  the,  384 

functions  of  the,  385 
Prehension,  98 
Presbyopia,  462 
Protoplasm,  2 

properties  of,  8 


Protonuclein,  72 

Prostate  gland,  470 

Pi'oximate  principles,  the,  60 

Pseudopodia,  3 

Ptyalin,  113 

Pulp,  the,  22 

Pulp  chamber,  the,  22 

Pulse,  the,  207 

technique  of  the  examination 
of  the,  207 

R 

Reflex  centres  in  the  spinal  cord, 

426 
Refracting  media,  the,  of  the  eye, 

452 
Reproduction,  464 
Respiration,  the,  219 

mechanism  of  the,  224 
types  of  the,  225 
nervous  mechanism    of  the, 
234 
Respiratory  oi'gans,  the,  219 

organs,  development  of  the, 
487 
Retiform  tissue,  structure  of,  18 
Retina,  the,  455 
Ribs,  development  of  the,  482 

S 

Sarcode,  2 

Sarcolemma,  25 

Sarcous  elements,  25 

Saliva,  composition  and  properties 

of  the,  111 
physiological  actions  of  the, 

112 
Salivary  glands,  the,  107 
Salts,  absorption  of  the,  177 
Secretions,  the,  281 
Semen,  the,  of  the  male,  468 
Senses,  the  special,  437 


INDEX. 


499 


Serum,  of  blood,  50 

of  blood,  treatment  with,  54 
Sight,  the  special  sense  of,  451 
Skin,  structure  of  the,  284 

glands  of  the,  286 

functions  of  the,  289 

development  of  the,  489 
Smell,  the  special  sense  of,  444 
Somatopleura,  the,  476 
Spermatozoon,  470 
Spermatoblasts,  469 
Sphygmograph,  the,  209 
Spinal  accessory  nerves,  the,  416 
Spinal   column,    development  of 

the,  481 
Spinal  cord,  anatomy  and  struc- 
ture of  the,  418 

gray  matter  of  the,  422 

functions  of  the,  424 
Spinal  nerves,  the,  429 
Splanchnopleura,  476 
Spleen,  the,  246 

Sternum,  development  of  the,  482 
Stomach,  the,  121 
Stomach-digestion,  the,  121 
Suprarenal  capsules,  the,  252 
Sweat-glands,    structure  and  ex- 
cretion of  the,  277 
Sympathetic  nervous  system,  the, 

"^431 
Syntonin,  71 


Taste,  the  special  sense  of,  441 
Teeth,  structui^e  and  development 
of  the,  100 
the  temporary  set,  103 
periods  of  eruption  of  the,  103 
the    superadded    permanent, 
104 
Testes,  the,  469 
Thymus  gland,  the,  251 


Thyroid  gland,  the,  250 
Tissues,  the,  12 

classification  of  the,  12 

the  epithelial,  12 
Tongue,  the,  116 
Touch,  the  special  sense  of,  438 
Trachea,  the,  220 
Trifacial  nerves,  the,  405 

ophthalmic   division    of    the, 
406 

superior    maxillary    division 
•      of  the,  407 

inferior  maxillary  division  of 
the.  409 
Tunica  vaginalis,  the,  469 
Tunica  albuginea,  the,  469 
Tunics,  the,  of  the  eye,  452 

U 

Umbilical  vesicle,  the,  476 

Urea,  255 

Urinary  organs,  development   of 
the,  489 

Uriniferous  tubviles,  the,  257 

Urine,  the,  263 

excretion  of  the,  267 
evacuation  of  the,  273 

Uterus,  the,  466 

V 

Yas  deferens,  the,  469 
Vegetables  as  food,  86 
Veins,  the,  191 
Vesicular  seminales,  the,  469 
Villi,  the  intestinal,  167 
Vitelline  membrane,  the,  464 

spot,  the,  464 
Vitellus,  the,  464 

W 

Water,  83 

absorption  of  the,  177 


500  INDEX. 

White  fibrous  tissue,  17  Yolk,  the,  of  the  egg,  462 

fibro-cartilage,  20 

Y  Z 

Yellow  elastic  cai-tilage,  19  Zona    pellucida    of    the     ovum, 

elastic  tissue,  18  464 


QP34 
/  Miiller 


M914 


/ 


